I thought of a way to solve this problem, that is to upgrade Mysql version to 5.7 or above.
The reason for this problem may be that I used to achieve full-text search in Chinese by rebuilding the FULLTEXT index of the database, but then the new server did not support full-text search function due to the lower version of MySQL, so an error occurred.
After I rebuilt the forum, I tried to transfer the website on two vps that also installed MySQL version 5.7. The result was very smooth and no data was lost.
I wrote my solution, hoping to help fellows with similar problems.
Finally, thanks to all those who are eager to help me. @luceos @datlechin