Outlook 2016 doesn't accept password or app password

I hope you're right, but maybe it's just that: hope. Went to bed yesterday evening, and all was good. Woke up this morning, and connection failure message was again present. Has since reconnected, but this may only be part of the vicious cycle we've all been going through. I do hope you're right!

I've noticed a change.

For the first several days of this issue, any of my 4 impacted accounts would connect and disconnect intermittently and randomly with no action needed by me.
Yesterday I noticed that 3 of my 4 impacted accounts disconnected and did not reconnect on their own.
Taking no action because I was expecting them to intermittently reconnect on their own, they stayed disconnected all day.

However, seeing indications, in the thread, of possible solutions being applied, I clicked the status bar in my outlook client where it said "Password needed" and all three of the accounts connected. 2 of the three used the stored password and connected and 1 required me to provide the password, but it also connected after I provided it.

All 4 of my impacted accounts remain connected as of this writing.

Yeah, OAuth not an option on my client, except for business accounts. What client uses OAuth 2.0 for personal accounts, that syncs everything?

This has been the only change I've made (Thunderbird), that has worked and stuck. Made it Monday 1/29, and no downtime. Other tools like 9Folders still up and down like a roller-coaster. Shame.

It's now 2 hours since my last app password failure, they've definitely fixed something in their servers.

But there's a lot in this whole sorry episode Microsoft deserve criticism for.