Now you're cursing me to read entire twitter threads?

This isn't in fact my hobby horse so without more specifics I'll just treat him as talking past people and move on.

Looking at the video in the second link, it looks like he only spent three minutes talking about trans people and I don't see any explanation there about how you're supposed to apply his universal biological definition to individual people.

It's in the second paragraph of one of the links I posted:

"It happens to be embryologically DETERMINED by chromosomes in mammals and (in the opposite direction) birds, by temperature in some reptiles, by social factors in some fish."

Most of the time!

Sometimes you don't get gametes. At that point, you either need to exclude those people from your classification system because it's ill-suited for this task, or you need to make your classification system significantly more complicated because there's a lot of edge cases.