As documented in this older thread, Set up reply by email with POP3 polling 9 years later, It seems that Google is shutting down IMAP / POP with username:password authentication in favor of OAuth.
- Access to LSAs will be turned off for all Google Workspace accounts. CalDAV, CardDAV, IMAP, POP and Google Sync will no longer work when signing in with just a password — you will need to login with a more secure type of access called OAuth.
source Is there any work in the pipeline to change discurse to reply by email using OAuth before Google deadline?