It may be not user visible and technically not a Plasma but Qt change but I find the work so that apps survive the compositor restarting amazing. See …davidedmundson.co.uk/…/qt6_wayland_robustness/
One of the most visible ones for me is that most common multimonitor workflows Just Work™ in the Wayland session now. There are still edge cases, but we’ve put a huge amount of effort into this.