What martial arts are suitable for thin people to practice? I am 170 cm tall and weigh 50 kg. My arm is weak.

Your figure is too weak. It is suggested to start with the basic skills of Wushu. Don't think about practicing martial arts yet. In the final analysis, training at home and abroad has the same purpose, all the same. If you want to keep fit, you can consider learning Tai Chi instead of looking for the old people in the square to do Tai Chi aerobics. Find a famous local master. Practice the basic skills of Wushu first. Then you'd better learn a set of foreign boxing and a set of domestic boxing. Learn Tai Chi after you have a certain foundation. After practicing Tai Chi for several years, I will learn from the master to understand the boxing theory. It is good for the world outlook and health.