There's more to biological sex than just genitals. So like if a biological male somehow loses his penis, the rest of his body is still male. So lesbians and straight males wouldn't be attracted to him. And this very point really bothers TRAs because they can't, or more accurately refuse to, understand it. Speaking as a lesbian, I'm attracted to the female body, including the feeling of their skin, the shape of their hips, breasts, even things like what their hands look like and of course, the vagina. In contrast, a male's entire body is a turn off even if he has no penis. And despite what TRAs claim transition does not get rid of all these traits. So thus, in your example of a transwoman who had SRS, whoever has sex with them is having sex with a male and would be straight, gay or bisexual accordingly. The sex act doesn't matter, only the biological sex of the individuals matter.