LED dimmers are like $3 on AliExpress, but yeah that's much more than a potentiometer. On the other hand they handle 12-24V and like 6A of current. You can sink that kind of power into a pot.

We set the potentiometer pin as 0 (A0 on the Arduino Uno board), the CONTROL variable is the voltage that is used to cotrol the led brightness of the speed of the fan. In the setup() function the ...