I found when migrating accounts when you go to select a microsoft account to migrate to but then select make a new account, it will make the account but then when it tries to migrate to said account it just 403s. The work around i found was make your microsoft account on microsoft.com and then to migrate without hitting create new microsoft account.

An easy bug fix for this would to just grey out the make new account button when migrating.

When i contacted mojang support they redirected me here, if i get redirected again i'm not going to contact them as they were not able to help me at all (I don't need help anymore as i found the work around myself)