@teto I have a Steam Deck but I only use it to play games and I rarely go to desktop mode. I do not doubt that the version of KDE in the Steam Deck has been made somewhat stable by Valve.
Every single time, we're talking 2 decades here each time when I've tried to use KDE (on my 1000% stable computers with no hardware issues) I keep finding bugs and crashes all over the place and what I do is not even do serious work on it, just attempt to configure it using its own preferences.
Sometimes the crashes are in component A, sometimes component B, sometimes the entire thing goes in flames. I do not do anything special, just deploy what is marked stable. Be it RHEL, be it Debian, be it Ubuntu or Arch and attempt to configure it.