If there's no such thing as biological sex, then how do trans people know they are trans? ?
I don't know where you have been, but there are tons of people who claim that biological sex is not real. It's PC science. Nicholas Matte to name one proponent.
But Time was judged guilty of using “a simplistic and outdated understanding of biology to perpetuate some very dangerous ideas about trans women,” and failing to acknowledge that biological sex “isn’t something we’re actually born with, it’s something that doctors or our parents assign us at birth.”
https://www.heritage.org/gender/commentary/transgender-ideology-riddled-contradictions-here-are-the-big-ones