I have been enjoying OpenSUSE Tumbleweed. It's a rolling distro unlike the Ubuntu and Debian derivatives, but the updates hardly ever cause problems and it's very easy to roll them back if they do. It also gives you a choice between X11 and Wayland, and Wayland is working well for me on Intel graphics.

I would recommend the KDE spin of Fedora.

Tumbleweed is pretty much the "official" kde distro

Fedora KDE Spin works pretty well

If you want something Ubuntu-based I'd recommend KDE Neon, last time I tried it, it was great. I don't think it has snaps since it's made by KDE.

Debian or MX.

Most likely the best distro for KDE is KDE neon, but that doesn't mean that much.

I use it on Debian testing and am very satisfied with it, KDE has never been so stable.

I'm using Kubuntu as my main OS and it has been very stable for me. You can remove snapd and install the deb Firefox repository. You should look up tutorials on how to do it, I did it and nothing broke

I for one hope to move from kubuntu to debian with KDE, I assume that won't have snap shit or systemd shit, but I might be painfully mistaken right there, I haven't checked it out yet.

I use it in Garuda. No complains.

Fedoras flavor with KDE. Fedora never caused an issue for me.

Endeavour switched to KDE as their main DE

Manjaro is pretty good.