Let me repeat a message i wrote some time ago here because i really don't think Flatpak is a good solution (note that this isn't issues from some ancient distro, this is from openSUSE Tumbleweed, this is only a few months old):

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Flatpak is awful, i tried installing software from it a few times and not only it always installs a ton of unnecessary stuff (practically an entire distro!) but also the software doesn't integrate seamlessly with the rest of the system. GUI software looks wrong (themes do not apply, font rendering is wrong), command line software doesn't show up in PATH. Example in [0] for the GUI bits (Bless for theme, Notepadqq for font rendering) as well as the disk usage for two simple programs like a hex editor and a text editor.

Even worse, while there is an option to install things in the user's directory only (so i can make a separate user to try some things that i can easily delete later) not everything installs with that options and wants root access to pollute the rest of my system.

Nowadays i simply avoid anything related to flatpak. If something doesn't provide normal binaries and i really want it, i'd rather compile it from source (and if the source language is something exotic or the program needs a ton of dependencies i'd just skip it).

[0] https://i.imgur.com/9tmo26J.png