Export the Mixamo character as FBX Unreal file (check when queue for download), then import with “T0 as Ref” the character and use the default Mannequin. The character then should work with Unreal animations. However, Mixamo animations are a bit off…and root motion is not working because Unreal root is on the ground, Mixamo between the legs. But when you export Mixamo with root motions as FBX Unreal, the Mixamo characters root motion should work, just not working with Unreal’s root motion system. Thus, don’t tick root motion inside Unreal for this specific animations. They are already root motions anyway. How you incooperate preexisting RM into your controller is another question, possibly through vector tracking.