On attempting to log in to Realms (first attempt ever), I get the Microsoft account screen. I enter my (existing, active) Microsoft account, and (next screen) password.

I now get a screen which has my photo top right, and in almost unreadable white font on light grey background (what!???!) has my email address. This page HAS NO QUESTION on it. It just has a date entry form. For all reasonable values of date entered, the form simply returns without any action or any error message or any other feedback. It is an infinite loop or infinite guessing game with no clue whatever as to what date value I'm supposed to be providing, let alone why.

This is a total failure from a UX point of view as well as a practical point of view and is totally blocking me and my family from using Realms. Frankly, Microsoft is terrible at authentication systems. Forcing all Realms traffic through the mess that is Microsoft authentication is just going to act like a massive traffic limiter. I like Minecraft more than I despair about using Microsoft's perennially broken authentication frameworks. But only by a very small margin.