you mentioned that file previews are broken for you, thy should just work, unless some component it terribly broken or missing…

Uhhhhh nope, that’s just the way it works.

…but, as a beginner, you shouldn’t even worry about this, as most distros provide easy-to-use, graphical app store applications that can automagically install apps

Yes I have the “Software” package manager. At best it is extremely slow, at worst it just doesn’t work at all. But it doesn’t come preloaded with many repositories, I had to manually load flatpak.