There doesn’t seem to be any xserver trying to start at all. What exactly are you seeing after boot?
Please try:
embedding driver into initrd:
https://forums.developer.nvidia.com/t/linux-mint-nvidia-driver-loads-with-startx-but-not-on-initial-startup/168262/2
disable wayland:
https://askubuntu.com/questions/975094/how-to-disable-wayland-in-17-10-in-gdm3-login-screen
reconfigure gdm:
sudo dpkg-reconfigure gdm
log in and manually start gdm:
sudo systemctl start gdm