No worries about those details. I had been throwing myself at that wall for days anyhow so I shared them. In general...
We are all supposed to switch to modern authentication by September and Microsoft has legal cover for issues with IMAP until then because they've warned us about that, however the severity of this episode and the one in January speak to overlapping larger issues which in turn make this issue harder to diagnose. Additionally, much of what I was speaking to is specific to Windows 10 with freestanding versions of Microsoft office 2021.
How to handle this depends on what software you use. In android "Fair Email" the app itself provided a built in method to switch the accounts; one pass per account and no errors since. Even as messy as Microsoft office Became I was able to create accounts with modern authentication.
If you have recent Microsoft products which support modern authentication I would suggest attempting to create an email account (for an existing email address) in one of those apps using its automatic configuration and watching to see if it is using "exchange. You might not be able to manually configure anything but that's what you'd be looking for. There are some sources describing which Microsoft products use modern Authentication but some of the documentation is unclear (vis-à-vis the mess I reported) and in The primary page for switching to modern authentication there is some unorganized writing which makes it seem that IMAP will continue to work Outlook although I think that's not the case. In any event try to configure an account with modern authentication which should end up using exchange rather than IMAP.