I can find no way to edit an existing address list. I can delete entries but not add new entries. The old address book has an edit tab which opens a dialog for editing and adding entries to a list.

Please stop filing bugs against the new address book until it is switched on by default, which won't be until at least Thunderbird 92. We're well aware of the many things yet to be implemented.

FWIW, you can get the edit mailing list dialog by right-clicking the list in the left-hand column and selecting properties.

I apologize for misunderstand the offer to turn it on - assuming you were ready for testing. I'll shut up until told that you want it tested.