lots of error messages about it not ejecting the external drives

FWIW, I too recently got a new Mac mini. Mine is a M2 Pro model and I have two external drive systems directly connected to its Thunderbolt ports: a WD MyBook Pro, & a OWC miniStack STX. In my case, powering down the mini also properly ejects all of the drives in both of these systems ... without any error messages.

You would see this error message because macOS is warning you that you disconnected an external drive or device without properly ejecting it first. This message is intended to protect your data and prevent damage to your device.

To stop getting this message, you should always eject your external devices before disconnecting them. Here are the steps to properly eject an external drive on macOS:

1. Locate the drive you want to eject on your desktop or in the Finder window.
2. Click on the drive to select it.
3. Right-click (or control-click) on the drive and select "Eject" from the menu.
4. Wait for the drive to fully eject before disconnecting it.

If you're still getting the "didn't properly eject your drives" message after following these steps, it could be a sign that there is an issue with the drive or your computer's USB port.

Alternately, you can create an AppleScript to eject these drives and have it be available on the macOS menu bar for easy access.

At this point, you may want to consider contacting Apple Support directly for further assistance with this. To do so, simply select the "Support" link on the lower left-hand side of this forum's web page.

What are the error messages?

Can you post a pic of the message/s?