The flatpak "app" system has always felt like amateurish techbro crap to me, but today I finally put my finger on why.
The website is loaded with how-tos for installing it & packaged applications ("apps"), but there's not even a hint of how to maintain, manage, remove, or update them.
It has a set of halfway decent manpages that *do* say how to do these things, but there's literally zero reference! You have to just know they exist, & you have to just know `man flatpak` is how you start.
The only reason I use flatpak at all is because, in Google's tightly controlled walled garden of ChromeOS, it's literally the only way to install Firefox.
Mozilla Support, "Run Firefox on ChromeOS": https://support.mozilla.org/en-US/kb/run-firefox-chromeos
