What you’re smelling is hydrogene sulfide. The catalytic converter is supposed to converter the hydrogene sulfide to sulfer dioxide which is odorless. If the engine isn’t running hot or there’s no excess fuel entering the engine such as from a leaking fuel pressure regulator, then the odor is caused from a defective catalytic converter.
If the dealer told you that the problem is with the catalytic converter, demand that they replace it under the 8 year/80,000 mile EPA mandated warranty.
Tester