Account keeps getting locked everytime my kid uses the Series X. How to fix?

[SvennoJ]

Every time my youngest wants to play on Series X and signs in to his MS account on the Series X we just get a message something is wrong with the account, fix it on the web. There is says the account has been locked due to suspicious activity and has to be unlocked again. We unlock it and then he can play.

This is becoming really really tedious and annoying. I can't get any answers from Microsoft why this keeps happening. Has anyone experienced the same and maybe know how to get out of this mess?

Maybe make a new account for XBox? Can you still use a non MS account to play on XBox?