About Canon 600D Jiugongge, please give me an answer

This thing is just a rough idea, as long as it is roughly at the intersection of the tic-tac-toe shape. The golden section is also a rough ratio.

You first use live view to open the grid lines, place the subject at the intersection, take a photo to see where the subject is, and then the viewfinder will be at the approximate position.

Photography has no rigid rules. It relies on creativity, including composition, lighting, and exposure parameter settings. Only when you are unexpected can you achieve something.