Bit of warning about KDE:

It is very customizable, but as a by product is also really easy to completely fuck up. The first time I used it (eons ago) I ended up removing the task bar and couldn’t figure out how to bring it back or launch programs.

Just spend a bit of time reading up on it and you’ll be fine though.

Fedora Silverblue.

Or really any immutable OS; they would have to go way out of their way to even edit system files, much less break the system. I just recommend Silverblue because gnome is really hard for an inexperienced user to break.

Bazzite and Chimera are “SteamOS-like” distros that are more focused on providing a game console like experience.

They’re immutable operating systems, and the primary UI is Steam. Definitely usable as a desktop PC but that isn’t really their target niche.