As for restricting access to files you could run them under a separate user account. User A shouldn’t have access to User B’s home folder. Although if its something that would need granted admin access I think it would have access to other users files again.
KDE does have focus stealing prevention, Have you messed with that at all? https://docs.kde.org/stable5/en/kwin/kcontrol/windowbehaviour/index.html#focus-focusstealing The only thing I can think of is maybe some notification steals the focus and doesnt give it back to the window.
I have a x1 carbon gen 9. Be very careful with the USB-C ports. I leave mine on my desk and my hub kept cutting in and out while using it and its gotten worse over time. I’ve seen others with similar issues and it seems like the fix is to solder on a new port. Its a work laptop so I just deal with it.
This happens on my Pixel as well. I forget which launcher I use but I keep the icon on my homescreen so I can just hold it to get the app info and force stop it.
Do they support port forwarding?
For tekken 7 if you bought the game through steam there shouldn’t be anything technical needed. Just hit install and launch it through steam should work. You might need to look up how to enable proton if its not enabled by default. I thought they were starting to do that. I’m not sure if you meet the minimum GPU requirements but you should be able to refund if not. For tekken 3 I don’t see a PC port, Your best bet would be setting up a PS1 emulator like duckstation.