Tilapia

In real life, tilapia are a group of edible fish originating in Africa that are notable for being primarily vegetarian, and also for being able to breed easily in lots of different water conditions. Records suggest that tilapia may have been raised as far back as 3,000 years ago, and they are commonly raised in tropical areas around the globe today. are the fourth most consumed fish in the world, after tuna, salmon and cod, two of which are already in Minecraft.
In the game, tilapia could spawn in rivers and lakes in desert and savanna biomes, as well as in ponds in villages. They could breed with kelp and seagrass, which would give more of a use to both items. Fish farms could be useful for players with bases in areas that don't have a lot of land for farming, but have a lot of water nearby. I don't think having a breedable fish would invalidate fishing either, because most players fish to get rare drops.
I think tilapia would be a good choice for a new mob, because it could represent diets around the world and fit the theme of the 1.20 update, while also being a useful addition to the game.