The female voice sounds more softer than a male voice

The female and male voice sound different, even if the size and shape of the throats are the same.
Vocalization is a form of exercise, and when basic sounds are made by vibrating the vocal folds they echo through 5 resonance chambers. Those moving muscles that are working are all soft tissues.
I’ve heard that the estradiol (a form of estrogen), which is a female hormone, makes connective tissue extend better.
In fact, the female muscles are softer than that of a male. That primarily, is why a female can move her vocal cord muscles and muscles related vocalization more easily as well as display more natural flexibility than a male.
Even if a male received female hormone injections, he cannot acquire a female voice quickly. This is because the male is not used to using certain muscles related to vocalization like a woman does. The flexibility needed is also lacking, and will take mental and physical training combined with patience to achieve.
Therefore, I recommend if you would like to change your voice, that you listen to your favorite female voice sing, and practice vocalizing over and over again. This training will cause muscle memorization, as well as build strength and flexibility in the muscles needed to produce similar sounds.
You have to let your throat remember how to move muscles without thought.

Happy boy and girl singing with closed eyes