Find My... Apple ID still associated with previous owner of Mac mini

I bought a Mac Mini on eBay months ago. The previous owner had restored the system to a clean copy of Catalina.

So I put my own Apple ID in, and migrate all my data from an older mini using Migration Assistant, and everything gets set up like a new machine. Nice.

Then I updated MacOS with a new system update today. After it rebooted and before it came to the log-in screen, it says this machine is associated with the previous owner's "Find Me" Apple ID as well as iCloud items and whatever. Apparently the previous owner didn't properly sign out of everything (or anything) before wiping the data. And it shows his em**l ad**ess which is, of course, unreadable.

I can send a snail mail to the previous owner since it's on the shipping box, but what can the previous owner do about the situation when the system has already been wiped and the machine is now here? Am I stuck with this machine being identified as still associated with his Apple ID??? There MUST be a way, right???? Apple MUST have thought of an easy solution to this seemingly very common problem, considering the multitude of posts about similar cases with various devices.