Disk Not Ejected Properly

Try these settings exactly as shown, might fix:

Great, thanks for updating! Additionally, avoid manual sleeping your Mac, instead use the Lock Screen settings to switch the display off on timer:

I had the same problem with my Seagate external mechanical drive. My other external SSD drives were not affected by this annoying error message. I finally solved the issue by ejecting the Seagate prior to shutdown. Upon startup (not restart) the error message ceased appearing after waking from sleep. For more details, see my post: "Disk Not Ejected Properly, Possible Fix?" of several days ago. I would be very curious if this works for you. Also, a Texan.

Does the external drive has its own power or it relies on the mac mini ?

Or do you use an external USB hub? (If so, again: is it powered externally - with its own power cable?

These are both considerations that can lead to such intermittances. It’s annoying.

In my case, even though the USB hub (and drives connected to it) have their own power, it happens.

Another consideration: when not actively used (meaning you are actively working on something on that drive - document, project), it may go idle and provoke that. Some drives are more prone to it than others.

Usually, if connected direct to a port of the mac, it tends to be more stable.

Also: usb-c ports, from my expetience, tend to be more stable then usb3 ports (i have both on a mini 2018. Not sure about the 2020)

You may also use fisk utility to check the external drive, just in case…

Shutting down overnight is no problem but as mentioned I probably have the mac on all day but may use it for a few minutes and then leave it numerous times a day.

Shutting down each time would be ridiculous but leaving it on permanently would also be worrying so the only middle ground I can see is sleep.

I'd strongly suspect...

A bad cable.

Drive going bad.

Drawing too much USB mA.

You can use Drive DX to possibly get a better view of Drive health…

https://binaryfruit.com/drivedx

System Settings>General>About, scroll down, System Report>Hardware>USB, what mA are used & available?

Is your drive connected via a USB hub?

Unless the hub is powered you can experience unwanted ejections.

You’re welcome 👍🤞

FWIW this is a 7 port 4 amp powered hub I bought last week for £23 and seems to perform well. It has an eighth port specifically for charging phones.

ATOLLA HUB

That's an interesting suggestion.

Most days I am using my computer all day long intermittently.

So I put it to sleep each time I finish, not just to save electricity but to preserve the machine . . . after all, if it's on there must be some wear and tear if only to the electronic components. That has been my rationale.

However, as the latest Macs have SSDs and therefore no physical wear, does keeping a computer switched on when idle result in any extra wear on its electrical components?

Later Macs take less than a minute to start up, so shutting for long absences and overnights with the display off on timer taking care of power savings for regular ON operation, is way better than sleeping.

Sleep is a (stubborn) hangover from the past - it serves absolutely no purpose today other than throwing up mystery hangs, kernel crashes not to mention related fodder for endless discussion. Avoiding is best.