I have various IMAP accounts which all work fine both from Outlook on Windows and from MailDroid, Thunderbird, Samsung Email, Windows 10 Mail, etc.
One particular email address gives a login error every time, both via autodetect and with manual input, despite my entering exactly the same values as on Outlook for Windows etc. (servers, user names, passwords, SSL/TLS port numbers).
I tested the setup against the Microsoft IMAP tester here https://testconnectivity.microsoft.com/tests/O365Imap/input and it passed. In particular there are no material SSL certificate issues.
The account works fine with Outlook for Android on a brand new Android installation (BlueStacks) but not on my ‘phone or tablet.
I have also tried (against my better judgment) using the non-SSL ports (which the email server supports) – same login error experienced.
(edited to remove superfluous/confusing material)