This is a common misconception based on an argument put forward my Milton Friedman. It’s based on legal cases where CEOs were taken to court for knowingly defrauding shareholders for their own personal gain (say, selling all of a companies assets of the company to a different company the ceo owns privately for a single dollar).
Friedman argued that these cases set precedent that meant all CEO were legally obligated to maximize shareholder value and could be held legally accountable for not doing so. Friedman was wrong about this, like many other things he said, as he was not a lawyer, nor a particularly good economist. No CEO has even been successfully sued for “failing to maximize shareholder value” despite some people taking Friedman’s work to heart and trying to do so.