Ostensibly a CEO owes a fiduciary duty to shareholders to protect their investment

But Musk took Twitter private, there’s no shareholders to please.

Private doesn't mean no shareholders.

There were $13 billion in loans, and private investments from other folks like Larry Ellison and Suadi Prince Alwaleed bin Talal as well as some private equity firms.

So yes, there are shareholders, and there are creditors, it's just that in the private equity world, "caveat emptor" applies, they are expected to be sophisticated and wealthy enough to not need the protections given to investors in publicly traded companies.