After testing, although utf8mb4 can store data in the database, there is still a problem: if there are expressions before and after the WeChat nickname, and there is text in the middle, only the front expression can be saved in the database. The expression at the back turned into spaces. After several twists and turns, I still used utf8 to save the string selected in the blue bar in the picture below. The string was de-processed on the front end to ensure that the user's nickname was not destroyed