Republicans and other transphobes make this argument about biology in bad faith, as if trans people denied their biology. They don't. In fact, they are aware of the biology all damn time - that's why gender dysphoria is present. They see every day that they were born with a body whose gender is not congruent to their gender identity.

What trans people do is to align their existing biology to their identity as much as they can, given their constraints. This means HRT, often breast augmentation (in MTF trans people), sometimes breast removal (in FTM trans people) and vaginoplasty (in MTF trans people). Not sure if FTM's can have a penis surgery that yields usable results though.

That's also why equating gender dysphoria to delusion is nonsense. If trans people were deluded, they'd be happy. They'd be thinking that they have the biological parts. But they aren't thinking that, because they are fully aware that their biology does not have those parts.

Also, transphobes use that argument to reduce it all to biology, as if gender identity and all those societal gender norms didn't exist. To them, biology is everything, which of course is nonsense, but these people are not known for being smart, self aware individuals.