Rotation – in its non initial but final form – is easy to describe.
Why folks make it so mysterious i don’t know. Conjecture will run wild…
In pc games you are used to moving the joystick (and screen character) as does a pilot flying a plane: in 3d. Up/down, forward/back, left/right.
After a while you learn to use your upper arm with forearm and hand (plus finger) joints to also trace a curve in 3d space in front of your nose. You cannot fly a plane without doing this!
Rotation -for real – is moving the “next support point” in the hand to that 3d point , per above, where it will be, once that to-be supported finger plays down (and needs the support).
This creates a pico-pull on the connecting tendon back on that finger still releasing from the last played note. The release io that pico-pull (as you fully release then extend the new finger) gives the feeling of slicing through butter, when timed “just right”. You typically need to do it for an entire ripped chord (or two) to feel it. Its a standing wave – out of phase by one half wavelength. (Ignore if too much data…)
It helps if you can alternate wrist circles too. It needs speed and “coordination”.
Just imagine playing a fast scale on a newborns head. You stroke…
Another metaphor! Old computer disc drives used to create an 3atom high air cushion between the fast-rotating magnetic disc and the fixed ( in 2d but not 3d) reader head. The head would bounce rapidly at these micro distances, synced to the tiny variations of pull/repel from the magnetism deposited “across the air gap”
Not telling you how to get there. Telling what it is (once you get there).