There is no practical answer to this question.
The Owner's Guide states 50 lbs but that obviously includes a good safety margin. In practice, it highly depends on securing the spare tight against the tailgate and where you drive. Offroad where the spare is moving up down constantly is much different that driving on a smooth road.
IMO, with a little care you can get away with a typical 33x12.5 but anything larger should have an aftermarket carrier, preferably mounted on the bumper.
BTW, it's not just hinges, the whole tailgate can warp.