There are some differences in sitting posture between male and female cats, but they are not dramatic and depend on the size and posture of the cat.
Generally speaking, male cats have longer legs and slender bodies than female cats, so they will be straighter and more stable when sitting than female cats. . Female cats, on the other hand, are more inclined to tuck their legs under their bodies and sit more comfortably and with a little more elegance. But these differences are so subtle that it can be difficult to tell a male cat from a female cat by sitting posture.
If you need to determine the sex of your cat, the best way is to look at its genitals. In male cats, the penis is usually visible around the scrotum, while in female cats, there is no such area. If you're unsure, you should consult a veterinarian or professional to help you determine your cat's gender.