To ensure games run well on Linux either via Native Linux builds or Windows games with Proton, part of the magic is in the Steam Linux Runtime. A new version of it, the Steam Linux Runtime 4.0 was recently put up with some pretty big changes.
What’s the point of it? It ensures Steam and games run through Steam on Linux work properly across all the many different Linux distributions. Another secret Valve sauce for Linux. Well, not secret at all but you get my meaning I’m sure.
the flatpak version is unsupported by Valve for a reason. there’s been a ton of problems over the lifespan of the flatpak. it’s usually highly recommended everywhere not to use that version.
I’ve been using Steam in a flatpak for a couple years now, I think. What ton of problems are you referring to?
too many small things over the years to go over them all in one post. some still relevant, some not. drivers, for one. no game mode, if I remember correctly. you might end up having issues with controllers, and VR is out of the question on the flatpak. some people have reported issues with permissions.
it’s enough of a troublemaker that Bazzite blacklisted the flatpak, I believe, and it can’t be installed normally.