This isn't strictly true, Zuckerberg has to act in the interests of the minority shareholders as well. He can't take a deal that helps himself while hurting all other shareholders.

Getting involved in button padding issues isn't one of those cases though. He can spend all the time in the world on that if he likes.

Not really. The role of the fiduciary is to act in the best interests of the organization, including seeking counsel and advice from experts. “I was doing what I thought was best,” is not an affirmative defense, and has been successfully argued to be a dereliction of duty in corporate and contract law.

That's irrelevant when discussing ownership. He owns 17% of Meta. That he retains control of 90% of Meta doesn't mean that he has the moral right to ignore his responsibilities to his co-owners.

No one has the moral right to do anything since the entire idea of moral rights is absurd. Yes, Zuckerberg has a duty to act in the best interest of shareholders. Courts have repeatedly ruled that good faith belief is all that requires. Unless you think his interest in button ui is somehow in self interest over company interest he didn’t do anything wrong.