You can open multiple maps with ActorPalette.
But its more to open Asset Islands or references.
For me, the best example is when you have an asset level where all assets are located, and artists have prepared examples of how to use them together. This way, you can easily look at the references and just click on the asset to drag it into your level.
https://docs.unrealengine.com/4.27/en-US/API/Plugins/ActorPalette/