I've run into the most strangest issue I have ever seen from launching an APP, on a Linux OS. FYI, this issue never happened on POP OS. But I must also be fair to state, that upon the very first initial launch of Flatpak Steam on Zorin OS 16 PRO, I did not run into any issues.
It was only after shutting down Steam, and re-launching it later, I discovered the issue. Also, restarting the computer didn't help the issue either. If I try to launch Steam from the GUI, either by clicking on the Steam icon on the panel, or by searching for the Steam APP in the Zorin menu, and clicking on it, it will log me out of the OS.
There is a way around this however, that I discovered from a Google search, and I wanted to post this method, for it might help other's out there. I still do not know what causes this issue, but a way around this, is to launch terminal, and type this in...
flatpak run -v com.valvesoftware.Steam
This will allow you to launch Steam. I will admit, in the pages upon pages upon pages of text in terminal after launching the APP, I do see sporadic errors in different places. But you know how it is, when you don't know what to look for, and what the real issues are, many of those errors is just a bunch of mumbo jumbo.
I am also having trouble getting a brand new game to launch, but I think its just that game, cause I have been able to launch a different game so far without issue. And Serious Sam Siberian Mayhem, has some reported issues already so, like I said, I think its a brand new game, that has no proper Linux support right now, and I guess I just have to wait on the fixes.
Again, I don't remember having this issue on POP OS with ability to launch Flatpak Steam. And Flatpaks are supposed to come with all required libraries already. So, I don't really expect anybody to help me fix any of this, this is more of a PSA, just letting you know, this could be an issue for you, and how to get around it sort of deal.
I am going to test some other games of mine and see if they launch and play OK. But in regards to SSSM, it looks like its just having issues detecting my GPU, and it just crashes upon launch. I've seen this issue before with older games on Steam. I am going to report the issue on PROTONDB, hoping for a fix.
But yeah, weird issue regarding launching Steam ha? Go to launch Steam, it logs me out of the OS, weirdest issue I have seen so far on Linux. So ya, I just gotta launch Steam via terminal, then it doesn't do that. I won't lie to you, these issues I keep having with Linux really frustrate me to no end.
Most beginners to Linux would give up and switch back to Windows by now. But I hold my resolve cause I never want to go back to Windows ever again. But even I know, all my issues would no longer be an issue if I were on Windows.