just a side note... if you are not eager typing the commands for stopping and starting the displays server every time, feel free to define short nice aliases (e.g. in /root/.bashrc file)
e.g., you could try those (self-explanatory) aliases.
obviously, make sure that you do not define aliases that have the same name as existing commands in /usr/bin or /usr/sbin
alias updd='apt update && apt full-upgrade -d'
alias stop_dm='systemctl stop display-manager.service'
alias start_dm='systemctl start display-manager.service'