Yeah there was a whole movement back in 2008 that tried really hard to prove that Michelle Obama is a man. It’s really weird even by conspiracy standards.
It’s not so weird, it’s just that right-wingers have no imagination, and so many of their smears are of the I-know-you-are-but-what-am-I variety. (ETA: See also, the “Joe Biden has dementia” thing.) The “Michelle Obama is a man” thing came about because a lot of people used to joke that Ann Coulter is a trans-woman because of her prominent Adam’s apple. (Which she really does have.)