To get an idea of the UE 5.2 IK retargeting workflow, start with the project template: Games > Third Person. This guide describes how to retarget to the UE5 Mannequin rig and it can be applied to any other rig the same way.
Create a MoveOne folder where you will store MoveOne data
Import the move-one.fbx, check Import Animations
In the Windows explorer (not inside Unreal Engine) Copy IK_MoveOne.uasset to the created MoveOne folder of your Unreal project
If you're working inside the UE template project "Third Person", open Content > Characters > Mannequins > Rigs > RTG_Mannequin. If you're working in your own project, create an IK Retargeter and a target IK Rig files and setup them accordingly to UE documentation
In the Source IKRig Asset, select the IK_MoveOne file
Set the Retarget Pose to T Pose
In the Preview Scene Settings change the Preview Controller to the Use Specific Animation and select the MoveOne animation sequence
To remove bone mapping artifacts, click Auto-Map Chains and select Map All (Exact)
Download IK Rig asset here
Video tutorial:
Here is also a video of how the IK_MoveOne.uasset file was created. This will be helpful for users who want to create their own IK Rig assets: