Apple Mail and AT&T OAuth

Yesterday, all of a sudden I couldn't get my AT&T mail on my Mac but could get the same mail on my iPhone (and at att.net). My Mail account went Offline and I kept getting an indication that the login and password were not valid even though I hadn't changed anything (Mail Connection Doctor).

(AT&T had advised last year that certain Mail apps would need to be compliant with their OAuth security; at the time they didn't really explain when or how we would be affected and nothing happened so I forgot about it.)

I searched their site again and found that by following these easy steps to Create a Secure Mail Key, my Apple mail immediately worked again on my Mac! It appears they have finally invoked the OAuth security requirement:

https://www.att.com/support/article/email-support/KM1240308/?authNState=Y&haloSuccess=true

btw, I still use my password in iPhone Mail; this Secure Mail Key is only required for the Mac. I don't think it matters which MacOS you're on. Im on Big Sur and this happened long after that upgrade.

Hope this helps those who had questions about OAuth - the thread was too old and I couldn't post on it.