Did you know that Deep Warm Ocean biomes don't generate naturally in Minecraft? This finally implements them so they can.
I wanted to build an undersea base deep below the surface with a big glass dome amidst a coral reef. Then I found out that while all four of the other-temperature oceans (lukewarm, ocean, cold, and frozen) had a "deep" variant, warm oceans - the only oceans with coral reefs - were unfairly left out; deep warm oceans do not generate. An unfinished version of them exists already in Minecraft's files, but it can only be seen in buffet-type worlds and it's missing the crucial coral reef part.
To find and visit a deep warm ocean quickly in your world, use this command in the overworld: /locatebiome deepwarmocean:deep_warm_ocean followed by /tp 0000 ~ 0000, replacing the 0000's with the coordinates displayed in the chat by the previous command.
Admittedly, I have no idea what I'm doing; I just used MCreator to make a super-simple mod that injects a sparse "dummy" biome into Minecraft's Overworld and then snuck a single-file data pack into the .jar that changes that dummy biome into a deeper version of the naturally-spawning warm ocean biome, complete with coral reefs. All I can say is this mod works as expected when tested on a new world, including when others' biome-adding mods are loaded.