Yes, I've retargeted before.
In order to retarget anything I need the OG skeleton asset, otherwise the engine cannot map the original bones on to the UE5 bones. Right now I cannot even watch the animations play in editor. The problem is the "from one skeleton" part of the "from one skeleton to another". In order to retarget to UE5 I need the skeleton they shipped with. Your asset that I gave you money for doesn't include it or includes some kind of broken version of it. I realize now it is kind of my bad purchasing a years old pack for UE4, but no one can help me obtain the original skeleton except you.