It was the kind of brazen PR stunt Jack Ma might have dreamed up. But this wasn’t the flamboyant Chinese billionaire who disappeared from public view eight months ago. It was Mark Zuckerberg, bobbing up and down on a hydrofoil surfboard, clutching an American flag and exuding all the confidence of a man worth $130 billion. The contrast between the social media mogul’s July 4 Instagram video and the day’s big event in China could hardly have been starker. Regulators in Beijing had just hours earlier banned Didi Global Inc.’s ride-hailing service from app stores, delivering their latest hammer blow to an entrepreneurial elite that once seemed destined to challenge Zuckerberg and his U.S. peers at the top of the world’s wealth rankings.