Microsoft announced that Basic Authentication will be turned off in Exchange Online for Exchange ActiveSync (EAS), POP, IMAP, and Remote PowerShell starting October 13, 2020. Basic Authentication (also known as proxy authentication) is the process through which apps are sending username/password pairs with every request made when connecting to a server, an endpoint, or an online service, with the credentials often being stored locally on the device. Microsoft plans to disable Basic Authentication and only allow Modern Authentication in Exchange.
Source: https://www.bleepingcomputer.com/news/security/microsoft-to-force-modern-auth-in-exchange-online-to-enhance-security/