Outlook 2016 doesn't accept password or app password

From not the community crew:

The Modern auth dialog used to have a problem that it would remember the last login name and can't revert back to change the login name for entering a second login name and then it's password.
And the are always several times reverting change between login.microsoftonline, account.live.com, login.live.com, ppsecure, oauth2 and etc while login the outlook.live.com and account.microsoft.com via the chrome.
Most of the time, the url parameter combination of the live.com and ppsecure have less problems than the login.microsoftonline and oauth2.
The Moden auth should be also a internet third certificate requirement method, will it also changes in the background of the dialog?

Old picture for refernce.

https://techcommunity.microsoft.com/t5/image/serverpage/image-id/173077i5CD51571E5C03050/image-size/large?v=v2&px=999
The simplest way to tell when using the Windows version is the very different authentication dialog each use. On the left below is the classic Basic Auth dialog, on the right in the mini web-like page Modern Auth dialog:

Hi Gabriel,

M365 plan here, most recent gmail app on most recent Android connecting via EAS.

The solution seems to get more and more stable. The number of password askings is reduced from everytime at the beginning to every hour to now about twice a day.

The apparent throttling issue with IMAP we were experiencing for several hours during the day today and evening seems to be much better and the slow behavior with folders and messages seems to be back to normal now. I hope it lasts and isn't just because there is less load.

Downdetector today (February 13) for Microsoft 365:

Aside from this, we have not had any further issues since January 31 with authentication prompt errors using IMAP/SMTP with basic/normal authentication, 2FA, and app passwords for Hotmail.com, Live.com, and Live.ca accounts in Thunderbird, Windows Live Mail, and Samsung Email clients.

Something has changed today (February 13) that has affected basic/normal password authentication using Thunderbird, Windows Live Mail, and Samsung Email clients with IMAP, 2FA and app passwords, for Hotmail.com, Live.ca, Live.com accounts that is causing the processing of folders to be very slow: opening and closing folders, checking for new messages, downloading headers and messages, marking messages read/unread, etc.. I observe that, while we are NOT getting repeated authentication prompt errors, it is really slow processing folders with multiple devices and clients.

After previous changes related to IMAP nearly 2 weeks ago around January 31, we had no issues until today using normal password authentication with IMAP, but something was clearly changed today that is really affecting functionality for us all of a sudden. Really disappointing because I had hoped IMAP with normal/basic authentication was resolved, until they apparently messed with something. It acts like the IMAP connections are being severely throttled.

Had it working for nearly the past 24 hours...then it stopped again. This has been the pattern for the last few weeks. Getting the following errors just trying to sync a calendar: