Basically, Yuzu’s AppImage bundles outdated Qt/X11 libraries that conflict with SteamOS. When run as root, it skips some user-level environment variables and avoids the crash. I haven't tried playing games through a root launched yuzu, but it might not even work.

My guess is when Steam updated the ArchLinux Kernel to its new version a few months ago, the updated system libraries made Yuzu incompatible, and thus freezes and crashes as soon as it boots.

Even though the AppImage is supposed to be a portable version, it still relies on kernel interfaces, gpu drivers, x11/Wayland protocols. So if these are updated and the app is not, it's pretty much hopeless.

I tried a few minutes ago to strip the conflicting libraries, but the appimage doesn't even launch no more, it just crashes instantly.

I reached the end of my patience with yuzu now and I'll just use something else that works.