Inform the user of nonfree Flatpak packages, like the commandline tool, and GNOME Software

[hamishmb]

I think MintInstall should warn about nonfree Flatpak packages like other tools do.

OS: Linux Mint 20.3 (in case it has changed since)
Version: 8.0.9

[haggen88]

Now Flathub has an option to filter out non-free software:

flathub-infra/website#1409
https://www.omglinux.com/flathub-website-free-software-filter/

[github-actions]

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[hamishmb]

Still not resolved with LMDE 7 and mintinstall 8.4.0. which is the latest at the time of testing.