Ours is a system of “checks and balances.”
The president can do this or that, but the courts and Congress can put a stop to it (depending on the circumstances and relevant rules). When the courts rule that the executive branch can’t do something, Congress can write a new law saying the president can do it. When Congress passes a law the president doesn’t like, the president can veto it. Congress, if it has enough votes, can override the veto. The whole idea is to deny any one branch or person too much concentrated power.
Everyone is supposed to have learned this stuff in grade school. But it seems a lot of people have forgotten.
Anyway, even under our system, each branch has powers that really can’t be checked. Congress, for instance, has sole authority to levy taxes and spend taxpayer money, declare war, etc.
The president has some unique powers too. Including the sole, final authority to grant pardons, which cannot be reviewed or repealed by Congress or the courts.