Demigirl is a gender, someone who is demigirl could identify as female or a female aligned gender and a androgynous/non gender like Non-binary or agender. Or if you want the Google definition; A gender identity term for someone who was assigned female at birth bus does not fully identify with being a women, socially or mentally.

What is demigirl?

Eh, that's your opinion

Not that I'm aware of... But to be completely honest, that sounds like a great idea

They're flags that represent different sexualities and genders in the LGBTQIA+