Mailbox import fails after Monterey upgrade

Well, I finally nailed the problem for anyone else encountering it. Having deleted my wife's email account and then reinstalled it, I should have selected that while still in System Prefs and checked the box for Mail. After I did that, it all loaded up just fine. So far so good!

Well, deleting my wife's internet account in System prefs just made things worse. First to appear was the box asking what kind of account (iCloud, exchange etc) and I selected iCloud. Then it asked for the email address and password, after which it crashed - I have included the error log that came with that! If anyone has any idea how to fix this, I'd be really grateful. I have tried restarting and logging out and in again.

I posted this over a week ago and you are the first person to comment. I still don't know what to do and would love someone more knowledgable to help us! I have done more research and this problem has surface several times before with Apple OS upgrades - I have tried some of the solutions posited then, but to no avail. I am told that I should delete the email account and then reinstall it - apparently you can do this from System preferences (as you can't get into Mail prefs), but I haven't tried it yet as we are not 100% sure of how to do it and are fearful of losing access to email.

Thanks for your response on this, much appreciated! We can still access email via iPhone and iPad (it's an iCloud account), so that is all still working. It's just that, since the OS upgrade, we can't get it on here MacBook Air. This weekend, I'm going to try and delete her account via System prefs (we can't get into Mail prefs) and then try adding it back. I will keep this thread posted on the outcome of that for the benefit of anyone else encountering this!!