Microsoft on-premises server product that runs Office Online.
As found on one forum, this issue can be worked around: https://www.reddit.com/r/microsoft/comments/xxg7qd/whats_going_on_with_the_m365_developer_program/.
However, after getting the prompt for the dev instance setup, the SMS verification can't be completed, as it never accepts a phone number, and I guarantee that my phone number is correct