They would freak out, especially donnie. then donnie would freak everyone else out even more by telling them all sorts of facts. april would probably stay in the lair and do online school, and donnie would probably go overboard trying to help her. the other turtles would go stir crazy and probably keep sneaking out anyway. maybe covid would be a good thing for the turtles. it would give donnie a chance to do college and not have to show himself. they would probably all be really bored tho.