Everybody knows that Minecraft Java edition will run on anything that can run Java, like a Raspberry Pi, for example. Well, you need a launcher to run Minecraft Java edition, and the Java launcher (which will run on anything) only supports Mojang accounts (see https://www.minecraft.net/en-us/download/alternative it still says "We got you covered!").

Contrary to what others said in this thread, I think that the communication has been quite poor for this use case, because the official communication insists on saying that the Java version will still be working, which is a lie: the Java launcher already stopped working for new customers (I met several people who bought Minecraft to use it on Raspberry Pi, and their money is lost, because their purchase doesn't allow them to create the necessary Mojang account), and it will also stop working for all existing accounts in a few weeks.

It was not so hard to decide to make is a FAQ and say "Sorry guys, we are dropping support for all the architectures which are not the top 3 ones, your game will stop working", instead of saying "Don’t worry – the only thing that’s changing is how you log in to the game! [...] Minecraft: Java Edition will stay exactly the same, and we’ll continue to update and support it in the future."