We’ve been working for some time with several partners to come up with ways to smoothly transition our many users from Basic authentication to something more secure: OAuth 2.0-based authentication, o...
Updated Jul 11, 2022
Version 3.0
Blog Post
Greg Taylor - EXCHANGE
Microsoft
MicrosoftDevOpsMaverick - great question. Unless the config allows for it (the same article you took the snippet from has a comment on that too), then the user will be prompted for creds. The user will need to log in, to the ADFS/STS-Of-Choice, consent if required, enroll for MFA if required. Then it will update the account to use modern auth.
But no, new profiles, or even the migrated profiles will not keep using ROPC. ROPC is used for a one-time transition to OAuth only. Once done, the device uses tokens and drops the creds. Same as for a new profile.
JonasBack as the blog says "The code to automatically migrate accounts to Modern auth will appear in an upcoming Apple iOS update. "
Yes, before October. No, I won't tell you which iOS version, or we'd have said that. 
Once we have confirmed the version it's in, we'll update the blog.