Make sure that you enable/allow some form or level of remote administration in your firewall configuration before running in/switching to the commandline only mode
To make the system boot up into commandline only mode without the desktop environment or window manager, you should be able to just use/run “systemctl set-default multi-user.target” as root.
To revert (making the system boot up back with the desktop environment and window manager again), you should be able to just use/run “systemctl set-default graphical.target” as root.