I recommend Fedora to everyone wanting a desktop alternative to Ubuntu. It's a well-balanced distribution that is opinionated enough to work fine as-is but doesn't try to force things on you the way Ubuntu does with snaps.
What DEs are common/supported on Fedora, I use KDE (Kubuntu), I'm not keen on snaps and so it seems expedient to switch distros when I next install (as it seems Ubuntu are all in for snaps).
Gnome is the default and there's a KDE "spin", but I use Sway myself so I can't really comment on how well KDE works.
Well, this is a KDE variant of Fedora Silverblue, so there are some quirks. If you want normal Fedora but with KDE, there is a KDE spin available: https://spins.fedoraproject.org/kde/
Whoops! Nice catch, I love Silverblue but forgot this was the Silverblue KDE spin.
I can't do that because I don't want to update every 6 months. If I wanted to do that I'd just move to arch/endeavour.
You don't _have_ to update every 6 months. Each release is supported for around 13 months so you can hop every 2 releases.