Again.
A prejudice is not necessarely an insult. A prejudice is an action that can be harmfull toward people.
In this case. Saying "a trans woman is not a woman" is :
- Delegitimizing the existence/identities of trans people
- Dehumanizing trans people
- Participating in the overall delegitimization of trans people
- Potentially directly harmfull to trans people who could see said messages
Literally, you saying "a trans woman is not a woman" is like me saying "you are not a human, you have no existence"
https://www.plannedparenthood.org/learn/gender-identity/transgender/whats-transphobia
About transmisia (transphobia):
Its worse than an insult !