Compatibility
Multiplayer
Blue Depths is entirely compatible with multiplayer, and is specifically curated for multiplayer use, especially with the boss The Nameless Depth.
Mods and Other Datapacks
Blue Depths should be compatible with most other mods and datapacks. From the beginning of development, Blue Depths was being built with the ability to work with other projects well. It isn't supposed to be a datapack that can be the only "modification" in your world.
Nonetheless, it is possible it cannot work with certain datapacks, or datapacks packaged as mods. What I would be suspect Blue Depths can't work with are datapacks that also add new creatures like sharks, but even then I tried to make sure that wouldn't be a major problem, and made it so that it could still coexist with other aquatic mob packs. The biggest potential incompatibility are datapacks that tweak drowned, whether it be by how they spawn, or modifications to the drowned themselves.
Datapacks that work especially well with Blue Depths
One datapack that was specifically made to work with Blue Depths is the pack Deep Blue: Ocean Survival by the creator FunkyToc. The creator was able to make Deep Blue handle mob spawning and other functionalities for Blue Depths mobs in their ocean world datapack. If you would like to check it out, check out the link: