I have made no changes to any server settings from before this all started Jan. 23, and I have been running several tests on older clients and systems including Windows Live Mail using IMAP configured to imap-mail.outlook.com with SSL/TLS using app passwords with normal authentication method (not OAuth2, etc.) as well as Thunderbird.
Where before, since Jan. 23, clients were experiencing intermittent yet consistent errors authenticating account logins, for the first time since Jan. 23, I am now having no issues at all syncing all accounts including *Hotmail.com, *Live.com, and *Live.ca, as we had no issues with these same configurations prior to Jan. 23.
Unless it is just a coincidence, it seems functionality has been restored for us.