Hello MPe,
nice to see you fixed your problem 
So you didn’t do a pkg autoremove. So you still have 2 GB of orphan packages…
It never caused problems for me, but I’m a big proponent for backups!
I got rid of this error by installing “murrine”
sudo pkg install gtk-murrine-engine
PS.
Boot environments for UFS are in beta (version 0.1), so it is possible but probably not advisable to use yet - I can’t judge…