see also:
https://discussion.fedoraproject.org/t/login-in-gnome-gdm-not-possible-an...
After system-upgrade to F39 I am not able to login into gnome with the
User I made the update.
if this is only Xorg related (cause wayland logins are working here) I guess this one:
https://bugzilla.redhat.com/show_bug.cgi?id=2239055