Google have announced they are stopping support of less secure apps in G Suite in Feb 2021. No new LSA connections will be allowed after Jun 2020.
Google have advised me that the email accounts I'm using for Bounce Processing and Email-to-Activity Processing are affected by this.
Google's advice is "For any other LSA, contact your admin or ask the developer of the app you are using to start supporting OAuth".
Are there any plans for CiviCRM to support connecting to IMAP or POP using OAuth authentication?