I have also been experiencing a similar bug, both with Exposure and the regular Spyglass. Here are all of my findings:

When using no shaders and opening a spyglass, or the camera from Exposure, the part of the screen through which one sees the overworld turns black. It reverts back to normal when exiting. Additionally, when pressing shift while using the camera, to show more options, the bug disappears, only to come back once shift is let go of.
The issue becomes worst when using shaders. I specifically tested it with a heavily modified version of BSL v10.1.3 (I called it The Lighthouse) which shall be linked below along with the modpack I am using. In detail:

The black square persists after leaving the camera/spyglass
Hovering over the camera placed on a stand while a black square is shown will hide it, until the cursor is moved off again. If the black square originated from the spyglass, hovering over the camera then off will change it to the black square which originates from the camera.
If chat messages are still visible while using the spyglass (because they were just sent) the bug will not appear, until all chat messages are gone. This does not work with the camera
If chat is opened while the black square is present, it will temporarily disappear, until chat is closed again, at which point the square will be carved out where the chatbox used to be.

Modifying the Scale Factor, Shader Scale Factor, or toggling Forced Linear Scaling does not fix the bug. Leaving it all on basic settings does not help either.

I hope this will prove useful.

— Signed
Crowford Hidden

Incompatibility with Exposure (1.20.1 forge at least) #91

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