So you added Kubuntu’s Plasma to your Ubuntu desktop.
Mixing Gnome and Plasma on the same Ubuntu, if not any distro, is something that is long been known at least anecdotally to potentially cause at least some annoyances, but not usually overly major problems. But everyone’s experience here seem to be different.
Snap won’t have an effect on this, it has no connection to your non-snap software or desktop setup. There is no “hard” dependency on Snap in Kubuntu per se, and definitely none in Plasma itself.
That seldom ever fixes things, and depending on what you removed, you most likely did not completely remove it at all (there are hundreds of packages involved).
Of course, knowing the actual errors you had might help.
As you have had problems on both Ubuntu and KDE neon (which is Ubuntu 24.04) , My initial thought is a combo of your particular hardware and Ubuntu-specific driver/kernel issues. Trying a non-Ubuntu distro can help verify, or at least running straight-up Kubuntu, instead of mish-mashing two full desktops.