I am using 1.16 version of structures. The server side config file exists but the client side does not. I have tried to copy and paste the server config into client, and it will work and spawn a few structures, but every time I have closed the game and restarted it, it erases it again.

Wait, it's not a bug. It's normal. You just need to use the .server file either for the server or singleplayer.