problem is in how lookAt is conceived. it “mirrors” the camera when facing the spherical north and south poles, so the object or camera looks never upside down.
BUT, while this is correct behaviour for a camera, it is not in my case.
GIven that gravity pulls bones and joints down, mostly aligned, if i rotate the parent bone towards the first child, that is just under itself, the intended lookAt behaviour makes the joints “spin”.
I still don’t have a solution, but I’m starting from here [Solved] OrbitControls max polar angle = Infinity?