OpenSUSE is very less recommended but I would suggest it
https://media.ccc.de/v/5012-the-first-encrypted-steam-deck-runs-opensuse#t=0
Also check out their AEON it is still in RC but worth looking out for. Meanwhile Fedora immutable can be used with Intel.









If you are tach savvy want to tinker look for NetBSD or Ironclad OS