Do US presidents have less fiduciary liability than CEOs?

Do presidents have less fiduciary responsibility than CEOs?

Yes. Presidents and CEO's are entirely different roles and have entirely different legal obligations. CEO's and CFO's have significantly more fiduciary responsibilities to investors, shareholders and board members. The president of the USA has responsibilities to uphold the constitution, act as the commander and chief to the military, faithfully execute the laws among a myriad of other executive tasks.

If a CEO were to "starve the beast" by intentionally increasing expenses and reducing income, wouldn't that be criminally prosecutable?

Starve the beast https://en.wikipedia.org/wiki/Starve_the_beast

Why don't the US Senate ethics rules like "QBT (Qualified Blind Trust) or specific approval" apply to the Executive and the Executive Cabinet?

CEO fiduciary duties are enforceable by shareholder litigation, while presidential duties are mostly checked by elections, impeachment, and courts, so accountability is weaker and slower.