I was given the task of trying to resolve a connectivity issue with our WHD implementation not picking up new email tickets. It was configured for IMAP/Basic and was getting authentication failure, which I believe is due to the shutdown of less secure apps access.
I was able to successfully configure OAuth and authorize it, but when I click save, I get a validation failed error.

The only thing I saw different from the Configure incoming email documentation was that my authentication page did not have the following: "Click Advanced, and then click Go To WebHelpDesk", I used the helpdesk email account to authenticate. I'm not sure if this is part of the problem or not.