Years ago, when it was leaked, a poster said this:
It is done currently using a pairing system, so it means that the remaster is running using both an Unreal Engine 5 project, and the old Oblivion one. For instance, new graphics are rendered in the UE5 project, but most of the gameplay/physics/etc is still done in Oblivion.
New engine as in an updated creation engine or new engine as in they finally gave up on creation engine
People are saying it’s UE5.
Years ago, when it was leaked, a poster said this: