Do people who normally write with their right hand practice writing with their left hand, will it improve their thinking or analytical ability or something? In addition to having one specialty, ...

It only improves the reaction speed and does not improve the thinking ability. Because normal people, the left brain is responsible for handling movements and the right brain is responsible for thinking. The advantage of being left-handed is that you can finish it with your left hand immediately after thinking with your right brain, without transferring your left brain. Actually, being left-handed is not good. According to statistics, the life expectancy of left-handed people is about 5 years shorter than that of normal people. If you can change it, try to change it to a right-handed habit. Don't practice if you're not left-handed. It's no use.