Minecraft everything underwater?

I would like to play a challenge in Minecraft where everything is underwater.

I saw that on a Youtuber and wanted to do it with a buddy too.

Here is the video of the youtuber

What exactly do you want to know? How do you generate such a world?

Yes, exactly, is that possible with a command or do you need mods for it?

You could generate a flat world if that's what you mean. You can also enter the command / fill *** *** *** *** *** *** water replace air. LG

I would have thought of a completely normal Minecraft world, is that possible?

Maybe there's a mod or a plugin for it. 🤷♂️

Yes there's a mod, but I wanted to play with a buddy and load the mod on the server and then I couldn't get it to work, something always went wrong. That's why I hoped that there would be a command.

LG and Thanks for the help

By generating the world and then typing / fill (coordinates delimiting the world you want to play in) water replace air. LG

Yes or so xD