Do you have to release brine directly into the seaside? What about long pipes with holes that go 50-100 kilometers into the sea?
There's no question of polluting all the oceans with brine. They get freshwater from the rain and the salt came from the oceans in the first place. We aren't net destroying water molecules.
That's a very theoretical point of view. How to maintain those pipes? In two or three years, they will be full of small mollusks and other seafood.
There are many sewer and storm outlets just like this all around the world already
Only the outside. The inside will be full of brine. Once the salinity exceeds a certain value nothing but extremophile bacteria can survive in it.