Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello James Blue
Good day thanks for posting in Microsoft forum community, it's our pleasure to assist on the above query.
Regarding the above query, I've done further tests on my end but I'm afraid it's not possible to archive the above. Once you add MFA method, the login defaults to verification or MFA method registered. However, I'd also suggest you submit this same query to our Entra Identity team as they are experts in this field to check whether this can be done through a conditional access policy. Please use below link to submit the query Microsoft Entra ID - Microsoft Q&A an agent will be able to respond to the query.
Thank you for kind understanding and have a great day.