Nope, the term got associated with the LGBT+ community but originated from the anime/gaming community. Also, It doesn't inherently relate to sexuality, it's more about opposite gender expression or aesthetics by males that look/feel more feminine and want to embrace it a bit more.
https://www.dictionary.com/e/gender-sexuality/femboy/
https://gender.fandom.com/wiki/Femboy
https://en.wikipedia.org/wiki/Femboy
https://aesthetics.fandom.com/wiki/Femboy
Every webpage says the same, originally it was an aesthetic/gender expression for more feminine guys, later it was inherited into the LGBT+ community, as most of them are homosexual, but not all.