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.
For me personally (Fedora 43 KDE) about 80% of unity games that don’t have a native build refused to run at all. No problems at all since I swapped to a non-flatpak Steam install.
OTOH I’m having trouble with pretty much all flatpak apps in some way or another… might just be my system that’s being weird.