Green’s Dictionary of Slang

(US gay) a female to male transsexual.

1998		R. Scott Rebecca’s Dict. of Queer Sl. 🌐 FTM — Female To Male, referring to a person who is Trans[exual].
2023		S. Ayad When Kids Say They’re Trans 48: This gay FTM boy character holds many parallels to the ‘pretty-boy’ heart-throbs in a boy band.