Why the fuck does the president have authority to set specific IT policy for the government. He might not even have it, he loves making policies he doesn’t actually have the authority to make.

Because the POTUS is the chief executive. His literal job is to manage the executive branch of the government. Unless his policies go against the law, there isn't anyone who can legally dispute his policies for the executive. And if he does something illegal, the Senate can impeach him.

At least, so goes the theory.

Who else should have that authority?

Unlike Europe, the USA is not a technocracy. If you want to learn more about the 3 branches of government and the scope of their powers, ask your AI.