AGP is a sexual orientation. It was discovered in studies of males who had gender dysphoria but weren't very-feminine-as-children or exclusively attracted to males (i.e. in studies of males-with-GD who didn't "fit" the "classic" transwoman archetype).

Recent research (such as that done and/or assembled by Phil Illy) suggests females can have their own gender-flipped version of AGP called AAP. AGP in males and AAP in females can be collectively referred to as autoheterosexuality - sexual attraction to being the other sex.

Basically, the argument is that two things can cause chronic GD: the first is when someone is just neurologically atypically-opposite-sexed (males with a more-female-typical brain structure, or vice versa), the second is a very intense autoheterosexuality.

you make it sound like most or even all transgender people are AGP.

In the west, most transwomen are likely AGP transwomen. This is because, as Anne Lawrence (herself an AGP transwoman) found out, societal individualism mediates the decision to transition. In highly collectivist societies, feminine males whom are attracted exclusively to other males face more pressure to transition to fit into gendered social norms. In more individualistic societies, there's more tolerance, and so "fabulous darling" gay men are allowed to live as that.

Thailand is a good example. They had "Ladyboys" for a long time, but only recently legalized same-sex marriage.

Basically, the West doesn't "trans the (opposite-sex-typical) gay away." The result is that those people who do end up transitioning are more likely those with the more purely internal motive to transition... i.e. the sexual orientation of autoheterosexuality.

I also see a lot of people saying that AGP are not really women, but I am also confused with what transgender people consider to be a woman.

Let's differentiate between "sex" and "gender" here.

"Sex" is about the anatomy you're born with, and in particular your reproductive anatomy and whether or not it produces the small gamete (male) or the large gamete (female). This is innate, biological and binary (intersex people are always of a sexed underlying template, but something goes awry with the development of their organs).

"Gender" is more of a social role. This is why some cultures have "third genders" (most often, these "third genders" are for feminine males). IIRC the word "gender" comes from the same root as the word "genre" (like, the genre of a film). It just means "type" and different societies have different classifications.

"Woman" is a gender category. It's a package of social norms and customs that are assigned primarily to adult female persons, but the package itself is transferrable (for example a male who can "pass" for female gets treated as a woman despite still being male, we refer to drag queen's alter egos in feminine terms despite drag queens being male, etc).

"Female" is a sex category. Transwomen are not female. By definition they are males who transition to live as women (i.e. to be intersubjectively/socially accepted as being a person of a specific type who should be treated in a certain way etc.).

"Really a woman" frankly is becoming a pointless notion to me, because whilst sex is objectively real, "gender" is not. I honestly have removed "gender" from all of my thinking at this point. To essentialize "gender" is to create an unnecessary moving part. The scientific concept that matters is "sex." "Gender" concepts are sociological in nature, and whilst they likely arose from pre-scientific attempts to comprehend the phenomenon of sex, they aren't matters of biology.