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.