Office365: Client Credential Flow support for POP/IMAP is coming in June 2022
[Update]
Client credential flow is now supported:
https://www.limilabs.com/blog/oauth2-client-credential-flow-office365-exchange-imap-pop3-smtp
Microsoft is working on bringing OAuth Client Credential Flow support for POP/IMAP for Office365/Exchange. It’s planned to be released in June 2022:
https://www.microsoft.com/en-us/microsoft-365/roadmap?filters=&searchterms=70577
Check out currently supported OAuth 2.0 flows