The largest airport in the world is one. The busiest airport in the world is another. Just because an airport is large or the largest doesn't necessarily mean it's the busiest.
That said, the largest airport in the world is Beijing's Daxing Airport, a brand new one that will open this year. Before the construction of this enormous airport, the record was held by Erdogan's new Istanbul airport. The latter was built in a record time of just five years!
Beijing Daxing Airport. As you can see, it has a very attractive and modern design. But the choice to build it this way was also obviously for improved passenger flow. From the central point of the structure, all piers can be reached in the same time.
This is Istanbul Airport, whose control tower was designed by Pininfarina (below).
The number one airport in terms of passenger numbers is currently Hartsfield–Jackson Atlanta Airport, the capital of Georgia, which I'm reporting below.