Pansexuality isn't a legitimate sexual orientation. Sexual orientation describes the sex a person is attracted to: same, opposite, or both. Also known as homosexual, heterosexual, and bisexual, respectively. Pansexuals are bisexuals, but with a preference tacked on the end. Preferences have no place in a sexual orientation, and blur the lines between orientation and preference, which is harmful to everyone who's same-sex attracted (and opposite sex, though they're not as vulnerable). Bisexuality does not, by definition, exclude trans people (since they're still male or female), though plenty of bisexuals have preferences that exclude them, which is 100% fine of course.

Lately, woke bisexuals are pushing back against the idea that bisexuality excludes trans people and pansexuality includes it, because of the push that excluding trans people sexually is bigotry.

This take from the comments sums it up perfectly:

“Pansexual” is a clown label for someone who is bisexual, as there is no “all sexes” that somehow exists outside of a vulva or a penis. Intersex bodies aren’t even that common of an issue for it to be used to contest this, and intersex people are not a unicorn “third sex” that exist in droves to support the legitimacy of a supposed “pansexuality”.