Install GUI on Debian 11/12

Update the packages

sudo apt update && sudo apt -y upgrade

Install GUI

sudo apt -y install task-gnome-desktop

Update the run level

sudo systemctl set-default graphical.target

Reboot the system

To enable root login on GUI

Modify the file /etc/pam.d/gdm-password

sudo vim /etc/pam.d/gdm-password

Remove or Comment the line auth required pam_succeed_if.so user != root quiet_success

#auth  required  pam_succeed_if.so user != root quiet_success