I think this is why some members of his staff don’t want him to talk much right now. You just don’t know what’s going to come out of his mouth once he does.
That’s not to say that banning flag-burning is unpopular. To the contrary. It’s a matter of priorities, though. If there’s a plague spreading, and an economy tanking, and a raft of businesses being looted, the legality of torching Old Glory is a weird thing to be occupying part of your headspace.
Although, in fairness to him, it’s a recurring interest. Here’s what he tweeted three weeks after being elected president in 2016: