I recently Migrated my 6 year old account, i tried to login into Minecraft the next day on lunar client; it said my account was under the age of 18. So I went into the settings and changes that, then right after that when I tried to login it said "Failed to login:null". I am very disappointed that there a problem with the migration, they should have test this better. A lot of people are going to quit playing Minecraft. Now I lunched Minecraft with the launcher, it says when I hover over Multiplayer "Multiplayer is disabled. Please check your Microsoft Account settings". I navigated to:
https://account.xbox.com/Settings
I changed all the settings to "Allow"  Under the windows 10 section, and still nothing