Outlook 2016 doesn't accept password or app password

They don't need to roll changes per se, they just need to provide working patch.

Problem with whole thing is mix of old and new code and whole bunch of "cultural layers" which now is out of control. Outlook as program uses same tool of account management as it was in Win XP (may be not XP but 7 for sure) on top of modern or not so modern shell. Whole thing should connect to Windows account management and such. Corporate use different windows with different set of rules and privilege management. There is huge and fundamental difference between home windows log in and corporate server based log in. Not really my thing so explanation is bit vague here. Corporate did experienced fallout but was out of woods in 2-3 days. Personal e-mails are here and there. Web to my surprise on some logins suppressed MS advertisement (no complaints here) and on other did not. Same goes for some links in the e-mail body. My point here. Issue is more complex than it seems. I won't be surprised if it affected e-mails on certain servers (physically served by them) more than others. As much as it fun to guess there is no help in guessing. I wish MS would of cleaned the house like Apple did and provided actually new system. Changes to Office been more cosmetic in all 2013/16/19 and last 21. So i assume MS don't need to do that much to fix them all rather fix one and it will work on the rest.

I continued to use standalone Office because 365 was at mercy of developers thinking arbitrary changes in interface count as improvement in software. I had access to 365 for about 6 years and never was better experience.

That being said, it has not been "down". Webmail (accessible via phone browser) has been fine, albeit inconvenient, and bouncing network or cancelling password prompts has worked for most.

Running webmail your mobile browser is not reliable for when you are waiting for incoming emails or events. Power management at the browser level or OS level will choke the browser and connection, so you will not get incoming emails/data unless you are back on the browser tab and refreshing. This is not a solution, unless you keep that tab alive and constantly check it, you will not get timely event notification. Mobile browser has a lot more power savings techniques enabled, and I am not going to disable all those just so we can cuddle to MS' unreasonable stance of not rolling back whatever they changed.

You seem to have an unreasonable level of tolerance to MS issues. What next? Blame mobile email client for generating notification event for the password/auth error? And they should just go quietly? Or pretend it didn't happen? These are critical issue and naturally the client will throw a critical/urgent level event and notification.

You are right, the issue impacts the latest M365 version of Outlook. I added my personal Hotmail to my work Outlook, which is M365 with latest updates from the stable channel and it has this exact issue...over and over and over again. It was so bad, I removed my account from my work Outlook after a few hours. The password prompt has some type of "always on top" attribute and draws over all other screen elements. It also takes away cursor/pointer focus, so it's incredibly disruptive to normal workflow, so I had to remove it.

It looks like MS is still trying to apply small bandages here and there for what appears to be more of a systemic problem.

https://support.microsoft.com/en-us/office/outlook-and-other-apps-are-unable-to-connect-to-outlook-com-f4202ebf-89c6-4a8a-bec3-3d60cf7deaef

My Oauth mail account is functioning, but my calendar and contacts are not. And none of the suggestions you've provided are resolving the issue. My issues with TBSync were intermittent until this past Wednesday. Now they're constant, suggestion MS is making the problem worse, not better.

I really appreciate your time in answering my posts, but I again have to ask why MS hasn't just rolled back its untested changes that have caused this situation, and instead are leaving its users to flounder with a non-functioning service? It's unnecessarily frustrating for everyone involved.