But the world generates an normal, how to fix this?

You should set level-type to flat-minecraft\:paper_world. The names are weird since Minecraft doesn't allow numbers in the tags, and I couldn't think of a better name :P

For the moment the servers don't work (You will get a client moved too quickly error) I'll fix it when I'm free

Or you can install a mod like gottagofast to disable the serverside speed limit

Thank you,
You are The Best!!
want me to close the issue?

I'll close it 👍