I'm hitting a bit of a brick wall here.

Have setup a user with Microsoft 365 Business Standard as they wanted a custom email domain along with all the Office apps. Email domain etc is all set up and working no problem.

But they would like to log into Windows 10 (Pro, but not domain joined) on their laptop using their new Microsoft 365 account, but when I try to add them as a user on their laptop it says that it's not a Microsoft account. From what I can tell this is due to the fact that it's a "Work" or "School" account rather than a "Personal" one since they are on the Business plan with Hosted Exchange.

But surely I should still be able to use these logins for signing into Windows?