Microsoft has 2 different front-end web clients for email, as explained here, the newest is named "modern Outlook UI", and the former one is named "classic Outlook UI".
My Microsoft 365 subscription (and also my free old hotmail account) both re-direct to live.com and show the "classic" interface, even if I try to log in to office.com (and/or outlook.com).
My work account however, does the opposite - it redirects to office.com and shows a totally different user interface (which I assume is the "modern" UI).
How can I get my own email address which uses this modern UI?
I'm building an add-in, which I need to test under both UI's.
Here's screenshots which I think show the two?
classic:-
modern:-