I have 3 cats. 2 males one female. All adopted as kitten, all neutered as kittens. They are all adults now.
On rare occasion, the males will attempt to mount the female. There is no copulation taking place (in fact the males look rather clueless, as if not knowing what to do next), but the motions of grabbing the female by the scruff of the neck and mounting are performed.
The female also assumes the submissive posture for mating.
Never having mated and having been neutered before adult development, my conclusion was that sexual orientation/behavior must also be hard-wired into the brain. Hormones and glandular activity play a part…but it’s not the whole show.
This may also lend credence to the argument from homosexuals that they are "born this way."