No, French bulldogs are not hard to train. Like most bulldogs, Frenchies have a stubborn streak, but they almost always want to please their owners.
As a breed with average intelligence, French bulldogs can learn to obey most common commands with patient consistent training, and positive reinforcement.
In addition, they naturally have clean habits, so potty training is fairly easy. With that said, you’ll still need to be patient and kind because they may still have occasional accidents.