It would be handy for the next person who contacts Microsoft and where they do the fix to ask them what they did.  And I don't mean step-by-step.

I suspect the answer will end up being related to generating an application specific password (which really is, as Bill White has pointed out, more accurately described as a security key, but that's not what Google chose to call it) or to them tricking Outlook into running through the OAUTH part of modern verification.  But no matter what it is, it would be nice for the readership to have a broad description about what was necessary for the fix.
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Brian - Windows 10, 64-Bit, Version 21H2, Build 19044  

Here is a test to find out whether your mission in life is complete.  If you’re alive, it isn’t.
     ~ Lauren Bacall