Is the uobject class unable to overload the assignment function?

Are you tying to overload a comparison operator?
if so shouldn’t it be:
UVideoPlaybackParam& operator==(const UVideoPlaybackParam& obj){
//…
}
here you are just trying to overload the assigning operator = passing in the same type of object. So the setting of the parameter itself.

You can’t overload operator= for UObjects, it gets declared automatically in the generated file. See the macro DECLARE_CLASS in ObjectMacros.h for more info.