Hi there,
My understanding is that there is nothing impossible in Unreal. Have you ever tried to upload Manny to Mixamo.com and download it with a T-Pose animation? After importing only the animation to Manny inside UE5, save the animation as Pose Asset using right click + create pose asset, or directly inside the animation editor. Keep in mind that if you import the mesh with a new skeleton, the skeleton will come with root bone displaced at pelvis location, so this imported mesh is not usable for animations and gameplay. Perhaps you can use it for cinematics in sequencer. I’ve never tested it, but, in theory, it should work for retargeting your animations. Let me know if that helps.
EDIT: As uploaded to TPS Template:
