Unreal Engine’s FBIK solver allows technical animators to procedurally adjust runtime skeleton poses to react to dynamic gameplay inputs. This tutorial provides some insights into how to correctly configure the solver to achieve the desired pose.
This is for technical animators who are looking to get the most out of Unreal’s FBIK solver, in either Control Rig or IK Rig/Retargeter.
https://dev.epicgames.com/community/learning/tutorials/RByR/unreal-engine-how-to-tune-the-full-body-ik-solver