https://redmondmag.com/articles/2019/09/23/basic-authentication-in-exchange-online.aspx

https://techcommunity.microsoft.com/t5/blogs/blogarticleprintpage/blog-id/Exchange/article-id/27095

It plans to end support for Basic Authentication next year when used with various e-mail protocols, according to a Friday announcement. Those protocols include Exchange ActiveSync, Post Office Protocol (POP) and Internet Message Access Protocol (IMAP).   Additionally, Microsoft will drop support for Remote PowerShell when used with the Exchange Online service.

Support will end on Oct. 13, 2020 for those e-mail protocols, as well as for Remote PowerShell used with Exchange Online. In addition, Basic Authentication in Exchange Web Services will end on that same Oct. 13, 2020 date, as previously described more than a year ago.