How to put the Mac Mini to sleep (without logging in) when the screen is locked? The screen is locked after some time. That is ok. Then some minutes or hours later I come back. Sometimes I want to get in again, then I need to log in. But sometimes I just want to send the machine to sleep or to halt it right away. I want to do these without first logging in.
I disconnect the display in this case for sleep if I can't remember the shortcuts that I don't use often.

https://support.apple.com/en-us/HT201236



Option–Command–Power button* or Option–Command–Media Eject : Put your Mac to sleep.
Control–Shift–Power button* or Control–Shift–Media Eject : Put your displays to sleep.


For shut down, you can also log in - either via screen sharing, ssh, Apple a Remote Desktop or remote scripts if you need to sleep or power off the display and haven't memorized the commands above.