Stuck on System Administrator

You can restart from terminal:

Restart computers using Terminal on Mac – Apple Support

Please see this guide on how to restart your Mac from menu bar:

Shut down or restart your Mac – Apple Support

Maybe MacOS Keyboard Shortcuts can help you, if you want to use your power button, e. g.

Power button: Press to turn on your Mac or wake it from sleep. Press and hold for 1.5 seconds to put your Mac to sleep.* Continue holding to force your Mac to turn off.

Control-Command-Power button:* Force your Mac to restart, without prompting to save any open and unsaved documents.

Mac keyboard shortcuts – Apple Support

Every Mac has a power button. On portable Macs with a Touch ID button, press and hold that button until the Mac shuts down. That takes about ten seconds.

Then, start it again in the usual manner.