The article you linked is not disproving the finger-length ratio studies, it’s merely saying that some scientists disagree with it, while many others are convinced. It’s true that the measurements can be tricky, but your article says there are 1400 studies indicating broadly same thing, and many reputable scientists also agree with it.
To answer your second question, if large-scale studies were done, I suspect you would see more typically female finger ratios in trans women and more typically male finger ratios in trans men. Obviously, those finger lengths would have been the same as they were when pre-transition adults.
I know this is just one person, but my niece is gay and she’s in the air force. Her index fingers are way shorter than her index! Then there’s me, who’s ultra-girly, and my index fingers are way longer than my ring ones. My husband and my boyfriend both also have longer ring fingers than index.
We are on topic. Some posters don’t believe someone can be trans, so why should we use their preferred pronouns? I’m putting forward reasons why, one of which is a strong biological basis for sexuality and gender identity.
At the blob stage, genotype doesn’t matter either. It’s all waiting to be expressed later.