Thanks for your feedback!
Basicly yes.
Maybe not as foolproof as Mixamo yet, it’s sometime necessary to modify the auto-skinning manually depending on the character.
I haven’t tested retargetting with Mixamo rigs, but with Auto-Rig Pro you may need to adjust the base / reference pose so that it fits the Mannequin pose, when retargetting animations from the Mannequin for example. But should not be big deal. You can do this either in UE or Blender. Or you can adjust the rotation afterward by applying a rotation offset to the bones.
Here is an overview of the UE export from rigging to retargetting.
I’ll try and give feedback, should work normally.
The base rig is complex, but when exporting to UE / Unity you can choose the Humanoid rig type, which will export only the basic human bones, very light rig.
If the character is not a humanoid, simply choose generic and check Deform Only in the FBX params to export only the deforming bones.