>>264404982
IK bones are extra bones to help with animating
IK bones for a leg for example would allow you to place the foot in a position and the rest of the leg will automatically position itself in a natural way speeding up manual animation

VRchat has an IK system(code) which means when you only have head and hands tracking when you kneel down or move your body in your play space the IK system will place your legs naturally.

You're getting animation IK bones and the vrchat IK system mixed up. IK bones are unnecessary for vrchat.