Under the Constitution, the president has to be a natural born citizen of the US, a resident for 14 years (relevant in the early years), and 35 years of age or older. Any action to preclude a candidate has to be based on these qualifications. Art. II of the constitution spells out the powers of the executive branch. His primary power is to carry out laws enacted by Congress, therefore executive orders have to be based on some statute, or specific Constitutional authority (e.g. as commander-in-chief). No law allows the president to nullify the fact that Biden is a natural born citizen of the US, a resident for many time 14 years, and 35 years old. Congress has not passed a law declaring that Biden has been previously impeached and removed from office (another way to stop a person from being elected). There being no such authority, an order to that effect would not be legal. In addition, executive orders give orders within the executive branch, and the executive branch isn't in charge of certifying the next president: POTUS cannot give orders to the House of Representatives, or to the Supreme Court.