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 jumped into Tumbleweed recently and have really been liking it. Last time I used Linux with a desktop environment I was using Gnome and KDE was a lot unglier. Things have definitely changed.
KDE Neon gets the latest package updates regarding KDE first but it is not official in any sense, as listed on their website. In fact, Neon is just a package archive built on top of Ubuntu that offers more up to date KDE stuff.
I have used the distro as a daily driver in the past. It uses it's own pkgcon package management system.
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.
Debian does use systemd, but what's so bad about it? I'm just curious, I'm using Arch with KDE, and that also uses systemd. Never had any issues with it.
Debian doesn't use snap by default though.