I imported the CBP_SandboxCharacter from the new Unreal Game Animation Sample Project when I noticed that, unlike the BP_ThirdPersonCharacter Mannequin, the foot is “floating in the air” instead of “falling”
This is the CBP_SandboxCharacter:
This is the standard BP_ThirdPersonCharacter:
Is possible to implement this behavior? How can I do it?
Hey @Arystos! Welcome to the forum!
The answer here is that the sandbox character doesn’t look like it comes with IK setup. I haven’t loaded up that project before myself, but just looking, if you haven’t removed it then it must not come with it. Don’t worry though, that’s doable.
Here’s the documentation we have on IK and from there you can access multiple other pages like tutorials and in-depth setups! 
Hope this helps!
Thank you for your answer Mind-Brain, but I found a way easier path.
For anyone guessing I found the solution, and apparently is very simple:
I was looking in the default Animation Blueprint of the basic Mannequin to find clues, the original one uses the Control Rig to determine the Interpolated Kinematics but only when the Actor is not falling.
So I applied the Control Rig Node before the Pose History Node of the ABP_SandboxCharacter:
Once you create it you probably won’t see the Shoud Do IKTrace, that’s why you need to tell the node which Control Rig to use.
Open Details and on Control Rig set CR_Mannequin_BasicFootIK, and check the Shoud Do IKTrace in Input and Output Section
I wonder why is not implemented by default. I really suggest Unreal Devs put it in 5.5 
