MS likely consulted with their army of lawyers before pulling this.
Actions might be crappy but not illegal. Not a lawyer but employers are usually allowed to dictate the terms of the employment agreements and requiring someone to go into an office to work can be one of them. Even changing from permanent remote to onsite at a later time seems like another relatively protected decision.
Unless someone somewhere higher up is on the record saying something like “Oh yeah let’s make them come into the office to actually make it really crappy for them so they leave on their own” I doubt any reasonably reliable legal case can be made.