Outlook 2016 doesn't accept password or app password

Interesting sort of workaround... if you open outlook.com in your browser and log in, Outlook 2013 will stay connected and let you use it for your hotmail account...

It doesn't help much. If you look at your access history, you will likely see a mixture of IPv4 and IPv6 accessing your account, even on the same computer at the same time. The server doesn't really know if these are the same device or different devices.

Interesting sort of workaround... if you open outlook.com in your browser and log in, Outlook 2013 will stay connected and let you use it for your hotmail account...

That's a bit of a red herring. It's like slamming a car door a hundred times to see if the door will lock. The "chance connections" you are getting are not full connections. Microsoft has been crystal clear that, if you get connection now, you will eventually not get a connection as they are phasing out exchange server connection authentication that is not the newer OAuth or OAuth2. Since they have disabled the ability of Outlook 2013/2016 to update that authentication in Exchange servers, even registry hacks get re-written by Microsoft "security updates", or superseded by new keys in the registry.

Eventually they will force obsolescence of your POP and IMAP servers, supposedly to prevent hacking of your accounts. However, by people trying to keep repeatedly signing in to the exchange servers, they are unwittingly helping Microsoft with their efforts to prove how insecure they are and why all authentication should be updated. Because, IF you DO connect, you are helping Microsoft prove how hackers can log onto your servers if they try it enough times.

The really stupid thing is they could have, and should have updated this security without forcing everyone to use their servers and services. This will eventually be seen for the transparent money grab that it is, and, as I keep saying, I will be waiting for the inevitable class action.

In the meantime, be forewarned that POP and IMAP are both headed for obsolescence on Microsoft platforms. How soon? Nobody knows for sure. They've been talking about it for 3 or 4 years now. But rest assured, they will be happy to sell you cloud storage, not to mention regressive subscriptions. And those subscriptions will rescue you from the ignominy of controlling and organizing your own data on your own storage as, of course, it is better to pay for cloud storage.

Such a random affair: two of my four exchange accounts stopped working this morning in Outlook 2013. The other two are fine. Bizarre!

The only thing consistent about this issue is the inconsistency of the connection reliability. I've given up on Microsoft. I toyed with the idea of running Outlook for Android just for my MSA (Microsoft Accounts). But I noticed in order to get my contacts to show up in the phone dialer, I have to enable Contact syncs to device's Contact storage, which allowed a 2-way access. Similarly, Calendar is the same way. Unless you contain everything you do to within Outlook for Android, it's unavoidable to allow Outlook some 2-way access to the device's other information.

In the end, I decided to move 90% of data off Microsoft Accounts. I hate to say this, I rather let Google have my calendar and contact data than Microsoft. Google provides more values to me in exchange for similar access. Microsoft has demonstrated zero care for consumer privacy and the willingness to do whatever it takes to scrape user data. It's too much for me and I hope both EU and US governments would come in and slap them silly at some point in the future.