Tired of playing without boobs, what should I do? I have been waiting for the release of the mod for a new version for several days, I myself cannot figure out the methods and rewriting the mod for the new version, minecraft simply does not start.

You can use the Ears mod for this actually! It does not have jiggle physics, and they are not detailed, but that's fine for me and most players.
https://ears.unascribed.com/
https://gist.github.com/sylv256/a96b2c369e48ba50d9ed4d175033c693

Updated to 1.21.