Mac Mini restarts automatically after shutdown

This has been happening for a few months. (I have to run older Macs for Rosetta.) After the reboot, when I hit shutdown, it shuts down.

I looked at other forums and no one has an answer. The Mini otherwise runs fine. It's most annoying as I want to shut down and leave the office but have to wait for the reboot and then shut down a second time. Any ideas?