Speaking of Ubuntu-based distros with KDE desktop, I recently found a distro called "KDE Neon".
Well, actually, they themselves describe KDE Neon as "not quite a distro".
> Is it a distro?
> Not quite, it's a package archive with the latest KDE software on top of a stable base. While we have installable images, unlike full Linux distributions we're only interested in KDE software.
Anyway, I recently switched my laptop over to KDE Neon after my faithful FreeBSD install broke.
I have previously used KDE-based desktops on Fedora and on openSUSE. (And a lot of other DEs and distros over the years but the point was to speak about KDE.)
For my laptop I have been very satisfied with KDE Neon. Still debating whether or not to run it on my desktop.