, the game engine transforms .FBX into a unique structure (.uasset).
By @Serhat0101
its not that unique and its pretty easy to unwrap a unreal-asset back into a Fbx but yes that simple step covers you under the terms
so for example; I own BG3 and buy a mod from you that adds zombies
the file i get from you unpacks to add models/ animations [whatever] into my bg3 game = you are covered because I am assumed to not be a hacker and therefor need to go get my zombie model dirrect from Mixamo instead of your mod
if your mod also had a folder with Mixamo models or animations in Fbx, Obj [whatever standard you pick] then that would be against the licence because i could just use those models instead of getting them from Mixamo