diff --git a/build/psalm-baseline.xml b/build/psalm-baseline.xml
index 9b2187a267953..8d2bedba96725 100644
--- a/build/psalm-baseline.xml
+++ b/build/psalm-baseline.xml
@@ -3222,9 +3222,6 @@
     </MoreSpecificImplementedParamType>
   </file>
   <file src="lib/private/AppFramework/Utility/SimpleContainer.php">
-    <MissingTemplateParam>
-      <code><![CDATA[ArrayAccess]]></code>
-    </MissingTemplateParam>
     <RedundantCast>
       <code><![CDATA[(int)$e->getCode()]]></code>
     </RedundantCast>
@@ -4063,9 +4060,6 @@
     </DeprecatedMethod>
   </file>
   <file src="tests/lib/TestCase.php">
-    <DeprecatedMethod>
-      <code><![CDATA[$container]]></code>
-    </DeprecatedMethod>
     <InternalMethod>
       <code><![CDATA[lockFile]]></code>
       <code><![CDATA[unlockFile]]></code>
diff --git a/lib/private/AppFramework/App.php b/lib/private/AppFramework/App.php
index 5160fd61c83d7..1c6c30f23dc26 100644
--- a/lib/private/AppFramework/App.php
+++ b/lib/private/AppFramework/App.php
@@ -79,7 +79,7 @@ public static function main(
 		$profiler->setEnabled($profiler->isEnabled() && !is_null($urlParams) && isset($urlParams['_route']) && !str_starts_with($urlParams['_route'], 'profiler.'));
 		if ($profiler->isEnabled()) {
 			Server::get(IEventLogger::class)->activate();
-			$profiler->add(new RoutingDataCollector($container['appName'], $controllerName, $methodName));
+			$profiler->add(new RoutingDataCollector($container->get('appName'), $controllerName, $methodName));
 		}
 
 		$eventLogger->start('app:controller:params', 'Gather controller parameters');
@@ -88,12 +88,12 @@ public static function main(
 			/** @var Request $request */
 			$request = $container->get(IRequest::class);
 			$request->setUrlParameters($urlParams);
-		} elseif (isset($container['urlParams']) && !is_null($container['urlParams'])) {
+		} elseif ($container->has('urlParams') && !is_null($container->get('urlParams'))) {
 			/** @var Request $request */
 			$request = $container->get(IRequest::class);
-			$request->setUrlParameters($container['urlParams']);
+			$request->setUrlParameters($container->get('urlParams'));
 		}
-		$appName = $container['appName'];
+		$appName = $container->get('appName');
 
 		$eventLogger->end('app:controller:params');
 
@@ -139,7 +139,7 @@ public static function main(
 
 		$eventLogger->end('app:controller:run');
 
-		$io = $container[IOutput::class];
+		$io = $container->get(IOutput::class);
 
 		if ($profiler->isEnabled()) {
 			$eventLogger->end('runtime');
@@ -169,7 +169,7 @@ public static function main(
 				$value['value'],
 				$expireDate,
 				$container->get('webRoot'),
-				null,
+				'',
 				$container->getServer()->get(IRequest::class)->getServerProtocol() === 'https',
 				true,
 				$sameSite
diff --git a/lib/private/AppFramework/Utility/SimpleContainer.php b/lib/private/AppFramework/Utility/SimpleContainer.php
index 6246a56ac209b..68d15ef13a708 100644
--- a/lib/private/AppFramework/Utility/SimpleContainer.php
+++ b/lib/private/AppFramework/Utility/SimpleContainer.php
@@ -8,7 +8,6 @@
 
 namespace OC\AppFramework\Utility;
 
-use ArrayAccess;
 use Closure;
 use OCP\AppFramework\QueryException;
 use OCP\IContainer;
@@ -26,7 +25,7 @@
 /**
  * SimpleContainer is a simple implementation of a container on basis of Pimple
  */
-class SimpleContainer implements ArrayAccess, ContainerInterface, IContainer {
+class SimpleContainer implements ContainerInterface, IContainer {
 	/** @psalm-suppress ImpureStaticProperty A static property is the only way to pass the information from config to autoload */
 	public static bool $useLazyObjects = false;
 
@@ -254,36 +253,16 @@ protected function sanitizeName($name) {
 	}
 
 	/**
-	 * @deprecated 20.0.0 use \Psr\Container\ContainerInterface::has
+	 * @internal Used by tests
 	 */
-	#[\Override]
-	public function offsetExists($id): bool {
-		return $this->container->offsetExists($id);
-	}
-
-	/**
-	 * @deprecated 20.0.0 use \Psr\Container\ContainerInterface::get
-	 * @return mixed
-	 */
-	#[\Override]
-	#[\ReturnTypeWillChange]
-	public function offsetGet($id) {
-		return $this->container->offsetGet($id);
+	public function removeFromInternalContainer(string $service): void {
+		unset($this->container[$service]);
 	}
 
 	/**
-	 * @deprecated 20.0.0 use \OCP\IContainer::registerService
+	 * @internal Used by server container on app containers
 	 */
-	#[\Override]
-	public function offsetSet($offset, $value): void {
-		$this->container->offsetSet($offset, $value);
-	}
-
-	/**
-	 * @deprecated 20.0.0
-	 */
-	#[\Override]
-	public function offsetUnset($offset): void {
-		$this->container->offsetUnset($offset);
+	public function setInInternalContainer(string $service, mixed $value): void {
+		$this->container[$service] = $value;
 	}
 }
diff --git a/lib/private/Server.php b/lib/private/Server.php
index f54a9568e55cf..ad3692f1da3e3 100644
--- a/lib/private/Server.php
+++ b/lib/private/Server.php
@@ -781,8 +781,8 @@ public function __construct(
 			);
 		});
 		$this->registerService(Request::class, function (ContainerInterface $c) {
-			if (isset($this['urlParams'])) {
-				$urlParams = $this['urlParams'];
+			if ($this->has('urlParams')) {
+				$urlParams = $this->get('urlParams');
 			} else {
 				$urlParams = [];
 			}
diff --git a/lib/private/ServerContainer.php b/lib/private/ServerContainer.php
index 484f2647d2a65..0261e2996f4cd 100644
--- a/lib/private/ServerContainer.php
+++ b/lib/private/ServerContainer.php
@@ -89,7 +89,7 @@ protected function getAppContainer(string $sensitiveNamespace): DIContainer {
 					/* The application constructor will register the container, see App::__construct */
 					$app = new $applicationClassName();
 					if (isset($this->appContainers[$namespace])) {
-						$this->appContainers[$namespace]->offsetSet($applicationClassName, $app);
+						$this->appContainers[$namespace]->setInInternalContainer($applicationClassName, $app);
 						/** @psalm-suppress NoValue false-positive (see comment above) */
 						return $this->appContainers[$namespace];
 					}
diff --git a/tests/lib/AppFramework/AppTest.php b/tests/lib/AppFramework/AppTest.php
index 334eeefdab6c2..149c969e8d3fd 100644
--- a/tests/lib/AppFramework/AppTest.php
+++ b/tests/lib/AppFramework/AppTest.php
@@ -54,10 +54,10 @@ protected function setUp(): void {
 		$this->controllerName = 'Controller';
 		$this->controllerMethod = 'method';
 
-		$this->container[$this->controllerName] = $this->controller;
-		$this->container[Dispatcher::class] = $this->dispatcher;
-		$this->container[IOutput::class] = $this->io;
-		$this->container['urlParams'] = ['_route' => 'not-profiler'];
+		$this->container->setInInternalContainer($this->controllerName, $this->controller);
+		$this->container->setInInternalContainer(Dispatcher::class, $this->dispatcher);
+		$this->container->setInInternalContainer(IOutput::class, $this->io);
+		$this->container->registerParameter('urlParams', ['_route' => 'not-profiler']);
 
 		$this->appPath = __DIR__ . '/../../../apps/namespacetestapp';
 		$infoXmlPath = $this->appPath . '/appinfo/info.xml';
@@ -159,9 +159,9 @@ public function testCallbackIsCalled(): void {
 	}
 
 	public function testCoreApp(): void {
-		$this->container['appName'] = 'core';
-		$this->container['OC\Core\Controller\Foo'] = $this->controller;
-		$this->container['urlParams'] = ['_route' => 'not-profiler'];
+		self::invokePrivate($this->container, 'appName', ['core']);
+		$this->container->setInInternalContainer('OC\Core\Controller\Foo', $this->controller);
+		$this->container->registerParameter('urlParams', ['_route' => 'not-profiler']);
 
 		$return = ['HTTP/2.0 200 OK', [], [], null, new Response()];
 		$this->dispatcher->expects($this->once())
@@ -177,9 +177,9 @@ public function testCoreApp(): void {
 	}
 
 	public function testSettingsApp(): void {
-		$this->container['appName'] = 'settings';
-		$this->container['OCA\Settings\Controller\Foo'] = $this->controller;
-		$this->container['urlParams'] = ['_route' => 'not-profiler'];
+		self::invokePrivate($this->container, 'appName', ['settings']);
+		$this->container->setInInternalContainer('OCA\Settings\Controller\Foo', $this->controller);
+		$this->container->registerParameter('urlParams', ['_route' => 'not-profiler']);
 
 		$return = ['HTTP/2.0 200 OK', [], [], null, new Response()];
 		$this->dispatcher->expects($this->once())
@@ -195,9 +195,9 @@ public function testSettingsApp(): void {
 	}
 
 	public function testApp(): void {
-		$this->container['appName'] = 'bar';
-		$this->container['OCA\Bar\Controller\Foo'] = $this->controller;
-		$this->container['urlParams'] = ['_route' => 'not-profiler'];
+		self::invokePrivate($this->container, 'appName', ['bar']);
+		$this->container->setInInternalContainer('OCA\Bar\Controller\Foo', $this->controller);
+		$this->container->registerParameter('urlParams', ['_route' => 'not-profiler']);
 
 		$return = ['HTTP/2.0 200 OK', [], [], null, new Response()];
 		$this->dispatcher->expects($this->once())
diff --git a/tests/lib/AppFramework/DependencyInjection/DIContainerTest.php b/tests/lib/AppFramework/DependencyInjection/DIContainerTest.php
index bd82677200460..8a9e2729b944d 100644
--- a/tests/lib/AppFramework/DependencyInjection/DIContainerTest.php
+++ b/tests/lib/AppFramework/DependencyInjection/DIContainerTest.php
@@ -36,30 +36,30 @@ protected function setUp(): void {
 	}
 
 	public function testProvidesRequest(): void {
-		$this->assertTrue(isset($this->container['Request']));
+		$this->assertTrue($this->container->has('Request'));
 	}
 
 	public function testProvidesMiddlewareDispatcher(): void {
-		$this->assertTrue(isset($this->container['MiddlewareDispatcher']));
+		$this->assertTrue($this->container->has('MiddlewareDispatcher'));
 	}
 
 	public function testProvidesAppName(): void {
-		$this->assertTrue(isset($this->container['AppName']));
-		$this->assertTrue(isset($this->container['appName']));
+		$this->assertTrue($this->container->has('AppName'));
+		$this->assertTrue($this->container->has('appName'));
 	}
 
 	public function testAppNameIsSetCorrectly(): void {
-		$this->assertEquals('name', $this->container['AppName']);
-		$this->assertEquals('name', $this->container['appName']);
+		$this->assertEquals('name', $this->container->get('AppName'));
+		$this->assertEquals('name', $this->container->get('appName'));
 	}
 
 	public function testMiddlewareDispatcherIncludesSecurityMiddleware(): void {
-		$this->container['Request'] = new Request(
+		$this->container->registerService('Request', fn () => new Request(
 			['method' => 'GET'],
 			$this->createMock(IRequestId::class),
 			$this->createMock(IConfig::class)
-		);
-		$dispatcher = $this->container['MiddlewareDispatcher'];
+		));
+		$dispatcher = $this->container->get('MiddlewareDispatcher');
 		$middlewares = $dispatcher->getMiddlewares();
 
 		$found = false;
@@ -74,29 +74,29 @@ public function testMiddlewareDispatcherIncludesSecurityMiddleware(): void {
 
 	public function testMiddlewareDispatcherIncludesBootstrapMiddlewares(): void {
 		$coordinator = $this->createMock(Coordinator::class);
-		$this->container[Coordinator::class] = $coordinator;
-		$this->container['Request'] = $this->createMock(Request::class);
+		$this->container->registerService(Coordinator::class, fn () => $coordinator);
+		$this->container->registerService('Request', fn () => $this->createMock(Request::class));
 		$registrationContext = $this->createMock(RegistrationContext::class);
 		$registrationContext->method('getMiddlewareRegistrations')
 			->willReturn([
-				new MiddlewareRegistration($this->container['appName'], 'foo', false),
+				new MiddlewareRegistration($this->container->get('appName'), 'foo', false),
 				new MiddlewareRegistration('otherapp', 'bar', false),
 			]);
-		$this->container['foo'] = new class extends Middleware {
-		};
-		$this->container['bar'] = new class extends Middleware {
-		};
+		$this->container->registerService('foo', fn () => new class extends Middleware {
+		});
+		$this->container->registerService('bar', fn () => new class extends Middleware {
+		});
 		$coordinator->method('getRegistrationContext')->willReturn($registrationContext);
 
-		$dispatcher = $this->container['MiddlewareDispatcher'];
+		$dispatcher = $this->container->get('MiddlewareDispatcher');
 
 		$middlewares = $dispatcher->getMiddlewares();
 		self::assertNotEmpty($middlewares);
 		foreach ($middlewares as $middleware) {
-			if ($middleware === $this->container['bar']) {
+			if ($middleware === $this->container->get('bar')) {
 				$this->fail('Container must not register this middleware');
 			}
-			if ($middleware === $this->container['foo']) {
+			if ($middleware === $this->container->get('foo')) {
 				// It is done
 				return;
 			}
@@ -106,29 +106,29 @@ public function testMiddlewareDispatcherIncludesBootstrapMiddlewares(): void {
 
 	public function testMiddlewareDispatcherIncludesGlobalBootstrapMiddlewares(): void {
 		$coordinator = $this->createMock(Coordinator::class);
-		$this->container[Coordinator::class] = $coordinator;
-		$this->container['Request'] = $this->createMock(Request::class);
+		$this->container->registerService(Coordinator::class, fn () => $coordinator);
+		$this->container->registerService('Request', fn () => $this->createMock(Request::class));
 		$registrationContext = $this->createMock(RegistrationContext::class);
 		$registrationContext->method('getMiddlewareRegistrations')
 			->willReturn([
 				new MiddlewareRegistration('otherapp', 'foo', true),
 				new MiddlewareRegistration('otherapp', 'bar', false),
 			]);
-		$this->container['foo'] = new class extends Middleware {
-		};
-		$this->container['bar'] = new class extends Middleware {
-		};
+		$this->container->registerService('foo', fn () => new class extends Middleware {
+		});
+		$this->container->registerService('bar', fn () => new class extends Middleware {
+		});
 		$coordinator->method('getRegistrationContext')->willReturn($registrationContext);
 
-		$dispatcher = $this->container['MiddlewareDispatcher'];
+		$dispatcher = $this->container->get('MiddlewareDispatcher');
 
 		$middlewares = $dispatcher->getMiddlewares();
 		self::assertNotEmpty($middlewares);
 		foreach ($middlewares as $middleware) {
-			if ($middleware === $this->container['bar']) {
+			if ($middleware === $this->container->get('bar')) {
 				$this->fail('Container must not register this middleware');
 			}
-			if ($middleware === $this->container['foo']) {
+			if ($middleware === $this->container->get('foo')) {
 				// It is done
 				return;
 			}
diff --git a/tests/lib/TestCase.php b/tests/lib/TestCase.php
index f808947d4b75f..4a4ea3b728bc0 100644
--- a/tests/lib/TestCase.php
+++ b/tests/lib/TestCase.php
@@ -106,7 +106,8 @@ public function restoreService(string $name): bool {
 			} else {
 				// The service was not registered before the test override.
 				// Remove the test registration so the container returns to its prior state.
-				unset($container[$name]);
+				/** @psalm-suppress InternalMethod */
+				$container->removeFromInternalContainer($name);
 			}
 
 			unset($this->services[$name]);
@@ -368,14 +369,14 @@ public static function tearDownAfterClass(): void {
 		self::tearDownAfterClassCleanStrayLocks();
 
 		// Ensure we start with fresh instances of some classes to reduce side-effects between tests
-		/** @psalm-suppress DeprecatedMethod */
-		unset(\OC::$server[Factory::class]);
-		/** @psalm-suppress DeprecatedMethod */
-		unset(\OC::$server[AppFetcher::class]);
-		/** @psalm-suppress DeprecatedMethod */
-		unset(\OC::$server[Installer::class]);
-		/** @psalm-suppress DeprecatedMethod */
-		unset(\OC::$server[Updater::class]);
+		/** @psalm-suppress InternalMethod */
+		\OC::$server->removeFromInternalContainer(Factory::class);
+		/** @psalm-suppress InternalMethod */
+		\OC::$server->removeFromInternalContainer(AppFetcher::class);
+		/** @psalm-suppress InternalMethod */
+		\OC::$server->removeFromInternalContainer(Installer::class);
+		/** @psalm-suppress InternalMethod */
+		\OC::$server->removeFromInternalContainer(Updater::class);
 
 		/** @var SetupManager $setupManager */
 		$setupManager = Server::get(SetupManager::class);