My System is a Solus 3.9999999 updated to a 4.x Fortitude. Budgie. I removed lightdm and used GDM with gnome-shell because I wanted to try Gnome Desktop.
This Update right here kinda breaks something for me. It didn't start gdm at all. I have not looked into logs tho, I just wanted to have the system running again so I had to re-install lightdm and budgie and remove gdm/gnome-shell.
I also (re)installed slick-greeter, couldn't remember if it was necessary or not. The Update went fine after that and when I re-enabled lightdm service etc.
I will try to install gdm/gnome again later on. I will see if it works or not.