How to disable/enable GUI on boot in Ubuntu 20.04 Focal Fossa Linux Desktop - LinuxConfig.org

In the following article you will learn how to disable GUI on boot in Ubuntu 20.04 Focal Fossa Linux Desktop
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-disable-enable-gui-on-boot-in-ubuntu-20-04-focal-fossa-linux-desktop

hello I have installed cinnamon but at startup login user can choose between gnome (ubuntu) and cinnamon before login. How can i disable it so user can only login with cinnamon?