Let me think about that.... Ice is floating - then it melts and joins the rest of the Ocean. When water freezes to become ice the volume expands somewhat. So when ice melts it will take up less volume. The Ocean level will drop. Oh - my now what will we do????
I don’t think this is a huge deal either, but you are missing a key point. The ice is not currently sitting in the ocean. It’s about to fall into the ocean. That will displace some volume. For a while.
Something that big is going to cool some water. And that cold water is going to circulate, cooling down other stuff.
That’s how the earth seems to work. We are not going to change that.