That's generally false. But even if it's true, all the boss has to do is argue that medium-term profits will be generated by whatever policy they want to adopt. Since nobody knows the future, they might be right, and they're legally rock solid.

In other words, the duty to increase value produces unfalsifiable policy claims. So it is meaningless.

public companies do not necessarily have a Fiduciary duty to the shareholders, let alone one to increase value. Any that they did have (based on the laws and how they are incorporated in a given jurisdiction) would also be applicable to a private company. Private companies also have shareholders, the shares are just not traded publicly.

You’re probably thinking of the theory of “Shareholder Primacy” but that is a theory not a legal reality, although some insist it is based on a questionable interpretation of the precedent set by dodge vs ford motor company.

Public companies can be run in what ever way the board/shareholders see fit.

They legally don't. It's just expected.