Kubuntu and Ubuntu Studio both use KDE Plasma. Studio just has a lot more applications included in the base installation.
I used Studio for a while but they got messed up for a while and I don’t need all the video/audio creation apps anyway. I tried KDE Neon years ago but it seemed bloated. I have a mini PC with Debian + Plasma but Debian is always a step behind in updates. Good for stability though which is the point. That mini PC has freedombox on it and serves up my website.