Unable to import .abbu file to address book

Mac Address book is failing to import the .abbu file. I exported an .abbu file from contacts from an older Mac (running either High Sierra or maybe El Capitan, I don't recall). I no longer have access to the other machine as it was returned on a lease. Now I am trying to import the old address book into my current iMac and it's not working.

This isn't the same address book file that was transferred to my new Mac, I have another address book that is my main one, and what I'm trying to do is recover certain addresses from the old address book, by restoring the complete file to a separate Admin user account, so that I can then find the contacts I need, export them individually as vCards, and then import those vCards back into my main address book on my main user account.

I've tried opening address book first, then importing from the file menu. I've also tried double clicking the .abbu file itself. Both give me the address book dialog window choosing whether I want to "Replace All" contacts with the contacts from the .abbu file. I click "YES Replace All" and then nothing happens.

The new address book is empty, and nothing has imported from the .abbu file. I've tried several times.

Also searched for questions about this and only found old questions from years ago, none answered properly. I can't believe other people don't have this problem or don't know how to fix it.

Does anybody know what this problem is and how to fix it?

I also tried Safe Boot and it did not work either.

Thanks