I’ve been distro hopping for years. After each time trying a few distros, I always find myself coming back to Linux Mint (cinnamon desktop environment). It has everything I need, and just works beautifully out of the box. It might not be flashy or have the latest cutting edge features, but it’s stable.
I’m currently running the Debian edition of Mint (LMDE), and wishing I was back on standard Mint. Nothing major, but a few minor persistent issues that never happened on Mint.
I did try NixOS (immutable OS), but it didn’t seem to have support for all the apps I wanted. I gave up fairly quickly, so you’ll probably have more success.
Installing Plasma should be as simple as “apt install kde-plasma-desktop”, then log out and select plasma from the login screen. I’ve tried other DEs but not Plasma, so I can’t say for certain it will work.
You can always try distros in a VM almost completely risk free. It won’t tell you everything, but it’s an easy way to get first impressions without losing your main OS.
Edit: This forum thread says you can install and use Plasma, but it’s not a great experience. Mint will probably not be the right option for you then.