Just look at the photos on the computer. Usually, you should check the resolution of the monitor, which is the size you want.

Supplement to the question:

What I want to know is what size to choose on the camera and put it on the computer to see the most suitable size, not the narrow one.

The narrow display on the computer is only available when the camera is set to 16:9 and the monitor is set to 4:3.

Calculate the scale by the resolution of the display, and then set it to the same in the camera.

In addition, it is recommended to know a little about post-imaging software, such as the most convenient light and shadow magician, which is helpful to you.