That’s what the government wants you to believe.

I don't know the answer to this, but my grandma has an old microwave with a metal grill that your food rests on (like a rack in a conventional oven). I am not sure if it is the type of metal or the shape (it has a squiggly bend on each side, in the middle[0]), but it's definitely possible for metal to go in the microwave without sparking.

[0] very similar to this https://i.redd.it/7nakjihppwy11.jpg

I believe that depends whether it's actually tin or instead aluminum.