Does anyone know how to prevent a single board computer from always displaying a logged in terminal through the onboard HDMI port on boot?

I have a Tinker Edge T as a server, and it's running Mendel Linux which is a default debian-based OS recommended by the manufacturer. One thing I really don't like is the fact that if you plug in an HDMI cable and USB keyword, it will always give you access to a terminal as the default user, which doesn't even need a password to become root either. Is there a general Linux way to set a password for the GUI like you can on regular desktop Linux, or otherwise require authentication before you get a terminal or any other functionality, so someone can't just plug an HDMI cable and keyboard into the device and have root access to the entire device?