I currently use Fedora Kinoite and until Plasma 6 some major bugs will simply not be fixed. “Solved in Plasma 6” is a very common phrase now and that is okay.
But maybe once that is settled, I would like to have a system with tested packages, that doesnt always break and annoy me…
I love to see new features and especially KDE is simply best on modern Distros, currently. But with Nix and Flathub I think CentOS Stream should be a good mix?
I like the security settings it has, but I never used it. How good is EPEL, do external repos for things like Brave work? How old are packages, do you know when Plasma 6 will arrive there?
You should consider using distrobox and/or apx, so you can effectively run any software from any package manager from any distro.
You could have a bottled archlinux where you install and run cutting edge stuff.