Outlook in Gmail App

From: CHYRON (DSMITHHFX)22 Jun 20:28
To: ALL1 of 3
Who uses Windows and Android? I use Android devices, and set up my [work] Outlook 365 account in the Gmail app on my tablet and phone a few years ago (start of the WFH thang). Dead easy, and works like a charm. Until coupla days ago, when Gmail started asking for my Outlook credentials and basically won't accept the old, previously working credentials, or anything else. I have the Outlook app installed on both devices, and they have no problem with the exact same credentials but I'd rather not load a separate mail client, especially a resource hog like Outlook, when one will do.

Here's what I've tried:

User -- my outlook email
Password -- as above ^^^
Domain\Username: my outlook email (also tried mydomain\myemail)
Server: outlook.office365.com
Port: 443 (also tried 993)
Security: SSL/TLS

Yeah, those are the credentials that have worked fine for the last two+ years, until Monday.

AFAICT both devices have permission to access the account in Outlook settings.

I feel somethings changed and either Microsoft doesn't want to play nice with rivals, or some it's ham-handed new security dictat they 'forgot' to notify users about, because Google.

 (erm)
From: william (WILLIAMA)22 Jun 21:55
To: CHYRON (DSMITHHFX) 2 of 3
Yeah, I use both, but not in that configuration. So haven't had the problem. That said, I only use the gmail app on my phone for gmail -- so the problem wouldn't appear. Microsoft have been trying to steer all users at any level to using an MS account for several years. 
From: CHYRON (DSMITHHFX)24 Jun 13:57
To: william (WILLIAMA) 3 of 3
I managed to get it back by trial-and-error switching from an Exchange account (which Outlook 365 surely is), to a personal IMAP account where I didn't have to manually set it up. So perhaps MS is trying to steer enterprise customers away from gmail.