so I'll ask yet again, what exactly is transphobic about a sign, banner or t shirt that states Lesbian = Female homosexual?
Nothing in itself. It’s the intent behind it. The reason why there’re doing it.
It’s just another way to say “trans women are men” and you know it. We all know it.
It's stating the UK legal definition of the term "lesbian" as written in the Equality Act 2010:
Section 12: Sexual orientation
Effect
55.This section defines the protected characteristic of sexual orientation as being a person’s sexual orientation towards:
people of the same sex as him or her (in other words the person is a gay man or a lesbian)
people of the opposite sex from him or her (the person is heterosexual)
people of both sexes (the person is bisexual).
"A woman who is attracted only to other women is a lesbian."