I've been running Kubuntu for a decade, (including the dark days of of early 4.0, 4.1).
Kubuntu has been striking a nice balance of newish software, newish kernel and newish KDE
Though recent changes like the snapification of Firefox has left a bad taste. Might try OpenSuse KDE or Fedore KDE instead soon
Flatpak and AppImages has also changed the equation a lot, so maybe an old/stable base like Neon or Debian isn't so bad anymore