The warning is specifically for trans folk.

The government’s website issued guidance for transgender travelers, saying that U.S. ESTA and visa application forms require travelers to declare their sex, which should reflect their biological sex at birth. Travelers with an “X” marker on their passport or whose gender differs from the one assigned at birth are advised to contact the U.S. Embassy in Dublin for further information on specific entry requirements.

Ah yes, one of my favourite quotes by Orreleeise: “Overcomine challenges and oeeence ine teisge and rivively renence verover re rescience”