This should not be seen as advice for anyone but a very small number of people:

There is a good purpose for the flatpak. My use for it is Squad’s anti-cheat uses I think a depricated function in C, and the most updated version of glibc doesn’t support it anymore. The flatpak does contain a version of glibc that works, so I have two versions of Steam installed on my system. I only use the flatpak for Squad, because that’s the only game with that issue.