[Help] Multiple Steam accounts: KDE sessions and Flatpacks data separate?

Hello,

I recently got a Steam Deck and, since at the moment only my Steam account is logged in, I was wondering what happens when someone else logs into their Steam account: will the KDE session as well as Firefox's and Spotify's data be separate for their account or not?

My hunch is that it won't since as I understand it, Game Mode is completely separate from KDE and both seem to run with the deck user. Am I right?

Thanks in advance