A few other issues I encountered:
* Any time I need to reboot, it's delayed by systemd for 90 seconds while it's waiting for some session to complete?
In the past I enabled systemd startup for KDE, not sure if it's related.
* user level ssh-agent.service isn't kicking in, so I have to every time start it manually with systemctl --user start to be able to use ssh-add.
* Firefox causes plasma-browser-integration to crash on startup, but restarting it from the crash notification fixes it.
* wl-copy completely doesn't work with Plasma 6. May be it's by design?
There might be more, those are just some of the very obvious ones I hit when testing.
Regards,
Shmerl