The President can do plenty, they just can’t do everything and that’s a good thing. Trump did a lot of damage in his short time in office, but he could have done a lot more without the balance of power between branches of government in the US system.

That said, right now the gridlock is because the House of Representatives has a Republican majority. They’re the ruling party in that house, and you need that house to do a lot of things. They’re the party with “the most seats” while the Democrats have the slimmest of majorities in the Senate.