Minecraft on Switch: We are still working on a fix. However, for a temporary workaround, try not signing in to a Microsoft account. While you won’t have access to servers, Realms, or possibly Marketplace content, you will be able to play single player & split-screen worlds. - HZ

Came here to say the same thing... glad its not just us. Our game starts with 'fail to login to microsoft account' whenever we play minecraft on nintendo switch. Is this a known problem then (as well as it freezing the switch).