Yes, as far as I can remember, you will need to do retargeting. So put the animation from one skeleton to another.
There are a few tutorials and if you follow them, you will be able to use the animations on another skeleton.
Viewing post in Free UE4 Idle, Sit and Pose Animations comments
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.