My account is also a Microsoft acc. I can log in to the Microsoft account on the web browser on the same MacBook, but just not in the launcher. My other son uses an iMac with 10.13.6, logging in with his microsoft account hasn't been an issue.
I also have this issue on MacBook Pro, OS X 10.10.5
My account is also a Microsoft acc. I can log in to the Microsoft account on the web browser on the same MacBook, but just not in the launcher. My other son uses an iMac with 10.13.6, logging in with his microsoft account hasn't been an issue.