Minecraft World Built Entirely Underwater

As a Survival player I am well impressed with this. Amazing.

The world doesn't start underwater. You start a regular world and the new aquatic zones appear in the oceans and other bodies of water in the world. If you already have a realm or world created you must travel to a previously unexplored area for any of the
new aquatic content to appear.

If you play in a survival world like I do you have to make a lot of underwater breathing potion to really explore the deep ocean areas.

I would love to see an open world mm built off the concept that was introduced in the movie waterworld in 1995

where there are only a few spots of land in the entire game, where the sea level fluctuates and they move around depending on the shifting of the earth underwater, there would be cities built from rafts strung together and the would move around and change
depending on which vessels came together at any given time,

I would love to see it be a sort if game similar the the concept fallout 76 was based on where it's a open world type of game and is online but also allow players to play solo if the want or invite friends to play.

But I would want it to make things better where fallout fell short, ie; player support, updates fixing bugs, unlimited storage like the not online fallout games, having a story in addition to ever expanding sidequests and opportunities

There is a new craftable item that will allow you to build an underwater world. Once you have explored the oceans, and found some buried treasure and such, you should get the parts to build a conduit. The conduit will allow you to breathe underwater without
potions, in a given area. It is great for starting your own underwater kingdom to rule.

Which version of Minecraft are you using? It is the game itself that wouldn't launch or the world you have built before?