I’m looking for something simple that just works, with few crashes, few bugs and good community support. I’m moving away from Manjaro Cinnamon unstable branch to Ubuntu 20.04 and want a stable desktop environment. I only want bleeding edge software, but I want a stable foundation.
Any will do. I think all the major desktop environments are fairly stable. (If you you use the stable releases.) If I encounter bugs, it’s mostly in user software or hardware/driver related issues. I’m not sure if I would switch to Ubuntu 20.04, though. And if you already do all the stuff with the third-party sources, bleeding edge applications, I’d say the one or two annoying bugs in KDE over the years are the least of your concern.
I usually recommend getting a distro that somewhat aligns to your personality or usage scenario. But I’m not sure if it applies to you, since you’re set on mixing it with other sources and that will make the benefits you get from distro maintainers packaging the software meaningless. Maybe choose the recommended distro for your ‘third-party package manager’ and either of the destop environments it has good support for.