public abstract bool ApplyFootIK { get; set; }

This is equivalent to the "Foot IK" toggle in Animator Controller states.

This value starts true by default for Animancer.ClipStates (false for others), but can be automatically changed by Animancer.AnimancerNode.CopyIKFlags(Animancer.AnimancerNodeBase) when the Animancer.AnimancerNodeBase.Parent is set.

IK only takes effect while at least one Animancer.ClipState has a Animancer.AnimancerNode.Weight above zero. Other node types either store the value to apply to their children or don't support IK.

Documentation: Foot IK