I have a pretty comfortable Kubuntu 23.04 installation. I have run Debian in the past, What will I gain or lose if I clean install from Kubuntu to Debian (besides snaps, which is also a major inducement)
You will get the same version of Plasma and probably older versions of some other packages you use. With 5.27 being the last significant update until Plasma 6, you’re good on that for a while. Nothing will be newer than what you already have. None of your packages will get any updates beyond bug fixes and security updates, but it will be rock solid.
Kubuntu is also reliable and has newer packages. Personally, I don’t think there’s much to gain here unless you’re set on something that doesn’t have snap and don’t mind running older versions of most packages.
Others have mentioned the shortcomings already, but the real question is why do you want to switch to debian? If there's a particular reason you wanna switch go for it, maybe dual boot first to see how it goes, but otherwise there isn't much gained.
I'm also running Kubuntu, but I'll switch to EndeavourOS. I wouldn't pick Debian because I like having the latest versions of things as they're released, some things even in beta, but other than that I think it's a solid choice if it fits your needs.
I would suggest going straight Arch. EndeavourOS introduced a lot of weird things for me. The new Arch Installer is just text based but made everything so easy. Much happier now
I would second this. I’ve used Endeavour and it’s nice, but it doesn’t have much of a purpose. It’s an easy installer with some default packages. Once it’s installed, it’s 100% Arch but with a different name and you don’t know how some things work because they were automatically configured for you. Might as well use the real thing. The archinstall script is easy and you only have to do it once.
Fedora is your friend. Best of both worlds: not quite as bleeding edge as Arch, but rock sturdy and so far ahead of Debian in terms of up-to-date packages. I've been using it for years and never had issues.