Control doesn’t mean that you need a user interface or an account management. It merely means that MS needs to respond to a request like "I posted this comment,

Control doesn’t mean that you need a user interface or an account management. It merely means that MS needs to respond to a request like "I posted this comment, please delete it". Furthermore, under GDPR you don’t have to delete everything a user has written. Only personal information. Although it’s probably easier to just delete the whole comment.