Invisible Mac mini

For your Mac to locate itself, you need to have Location Services turned on. To fix location errors on your Mac, you need to turn on Location Services and enable Wi-Fi so your system can detect nearby network signals.

Enable Location Services

• Click the Apple logo in the top-left corner of your screen.
• Choose System Settings.
• Click Privacy & Security in the sidebar.
• Click Location Services.
• Turn the main toggle On.
• Scroll down to find Maps in the app list and make sure its toggle is turned on.

• If it is already on, turn it off, wait a few seconds, and turn it back on to refresh the service.

More info: Manage Location Services settings - Apple Support

Turn On Wi-Fi

• Mac mini computers require Wi-Fi to be turned on (even if you use an Ethernet cable for internet) because macOS uses nearby Wi-Fi network data to triangulate your physical position.
• Click the Wi-Fi icon in the top-right menu bar and make sure Wi-Fi is enabled.

One more thing: Check Date and Time

• Go to System Settings > General > Date & Time.
• Make sure Set time and date automatically is turned on. Incorrect system clocks block location verification.

More info: Change Date & Time settings on Mac - Apple Support

Is it connected to WiFi or Ethernet?

It needs WiFi for location services to work properly.

Thank you for the detailed advice. However, I have done all of those things numerous times including reinstalling the System all to no avail. All of my other Mac devices have no problems. My Mac mini just seems to be extremely shy. All additional suggestions are more than welcome. Maybe a computer psychotherapist is in order.