I'm having this same issue, only now, BOTH Microsoft accounts I own are affected, and I can't sign in with either. It's ridiculous that Microsoft/Mojang have failed to fix this issue after all this time. I'm going to reach out to support again and link them to this page, because they seemed to misunderstand the issue.
@Mega_Spud I hope Mojang fixes the clear account sign in data button in the profile menu, because it's all that stands between me and signing back into my account. I accidentally unlinked it and now the game won't accept the account when I attempt to sign back in.
@Willybumm4345 No idea if doing that will tag you lol but sadly that was my first thought months ago, and it didn't work.