command to switch base/root terminal

A session logged in as root is the system root user. It is a root shell.

If you want to switch to a differnet user, sudo can do that. See man sudo for details.

sudo -u username command

Enabling the root user is generally discouraged on macOS, and on others too. Use of sudo is recommended.

If you are trying to modify protected files, neither root nor an admin group user will help.

Neither root nor Admin group users can mofify protected files, short of disabling system integrity protection.

What do you mean by a "root" terminal? Did you activate the root user on your Mac? That is typically not done. Usually you just run Sudo with your admin credentials.

su can elevate your current terminal session to admin privileges.

This also is a bit of an "XY" problem. Tell us what you want to do.