The left one was taken by me and the right one was taken by someone else. Why are the results completely different? Is it a problem with the phone or post-processing?

Not only the post-effects and mobile phone effects, but also the part of the second picture, as well as the angle, that is to say, you have to find a "spot". Only those who have studied photography will understand it more deeply. , feel more carefully. If you want to learn this aspect, you can go to the wild to take pictures, or at home, try taking a picture from different angles to see if you can find the essence (funny)