TBT: We seem to have successfully migrated the old 2011 Mac Mini to the "new" 2018 one. Except for emails. They just don't want to move. We have asked a Mac Help Forum for assistance and advice. They have been really helpful with other problems, so I expect a good response.
We don't want to leave the old Mac Mini (it still works for posting and I am using it here now) until we solve the email problem on the new Mac Mini.
It actually does still work for most things like email and blogger. It's just that other apps are failing as they become unsupported on 32-bit and High Sierra. The new one is 64 bit Catalina.
We may be getting a grip on the email problem. When that is solved, we should be back online fully.
If the email migration doesn't work, we will still have them on this old Mac Mini and can play around trying migration things later. Actually, if the new Mac Mini receives new emails, we will probably start using it and keep the old one as archive. It costs nothing to keep it plugged in on a separate card table across the computer room.
Meanwhile, if we are still offline tomorrow, HAPPY NEW YEAR'S DAY TO ALL OUR FRIENDS, and hoping 2021 will be better than 2020!