>>285870448
Final IK kind of works with fbt but you have to work around. Use an unrigged dummy skeleton for your lower half, let vrchat move that, put IK follower objects on the feet etc, put Final IK script on the original weighted skeleton and have it target those ik follower endpoints.

Essentially an invisible fbt skeleton that vrchat uses as normal and then final IK solving for those endpoints. Twice as much performance cost for twice the rig, but who cares final IK isn't counted by vrchat's avatar performance assessment thing.