Reporting back to tell you everything went smoothly. I moved the gdm profile, updated dconf and rebooted. Everything is working fine and the dozens of warnings have disappeared. Thanks. 
sudo mv /etc/dconf/profile/gdm /root
sudo dconf update
sudo reboot now
I’ve described it a little bit in this old discussion. I’m coming from years of Ubuntu without ever feeling the need to dabble with the command line. Since I’m running Linux exclusively on my personal machine without a Windows drop-back installation and being not very experienced with all the details, using a rolling release distribution is really an adventure and made me slightly paranoid. 
I always triple check every command, document every system change in a text file and run a borg backup of my personal data and a timeshift backup before every update. I’ve met people using Linux who reinstall everytime they run into problems and I don’t want to be one of them. 
P.S. now that the vast number of warnings have disappeared, I noticed a couple of others which I’ll will deal with in a new topic.