I know it's super basic, but it comes down to sex - iirc, a poster once said what helped her believe that she identified as a woman was that when she thought about having sex, she fantasized about being penetrated, and for me, it's the opposite.
like, I know sex doesn't always involve penetration, especially when it comes to same sex couples, and it gets more complicated the more you look into things, but in the basest sense, I feel like I align more with the sex I was born as, even if it's only in that capacity.