Update: The full timeline for retirement of Basic Authentication in Exchange Online is now published in Basic Authentication Deprecation in Exchange Online – September 2022 Update.
In about 150 day...
Updated Sep 01, 2022
Version 5.0
Blog Post
Greg Taylor - EXCHANGE
Microsoft
MicrosoftDouglas_Henrique - Never heard of anyone using that. I'll try and find the team that own it, but it's highly likely it will stop working.
TheAutisticTechie - take a look at https://techcommunity.microsoft.com/t5/exchange-team-blog/understanding-the-different-versions-of-exchange-online/ba-p/3394487
haph3006 - Kiosk users can keep using OWA, and use POP with an OAuth2 capable client. Outlook is not an OAuth capable POP3 client when connecting to Exchange Online.
Greg-CNS - I have asked the Security Defaults team to consider allowing SMTP/Basic even when SD is enabled - but it's their call as to whether they do anything on that or not. One thought (not tested) - Outlook profile, there is a Security tab and a checkbox there to prompt the user for creds - is that something you've tried? Outlook: "Always prompt for credentials" is greyed out - Rocky Mountain Tech Team (rmtechteam.com) as it seems to be grayed out in recent versions.
MarkusDi - The Surface team are aware of a bug here. The basic auth attempt can be safely ignored (or blocked). It's a bug in the Hub OS, and will be fixed in a few months. It's trying basic even if modern is available, but shouldn't.