Polo shirts have three buttons, two buttons, and no buttons, but generally two buttons are more.
Polo shirts with two buttons are more convenient to wear, so there are more polo shirts with two buttons. If you only wear a polo shirt, then it is recommended to button the bottom button and leave the top one unbuttoned; if there are other ornaments on the neck, such as a necklace, you can also leave both buttons unbuttoned, so that it will not look so good. Hollow, but also to reveal their beloved decorations. If there is already a round neck T-shirt inside, and the two buttons are not buttoned, it is still quite good.
In short, except in more formal occasions, it is generally not necessary to button both buttons of a polo shirt.