I don’t know whether we have seen the eye before or not. However, from what I understand, the “eye” is just a spaceship with really really powerful hyperspace engines.
Also, Sabine Wren gave the darksaber to Bo Katan as she thought that she was more fit to be the ruler of Mandalore. The Armorer even shared her criticisms about this with Dinn Djarin in the Mandalorian. Now, we still don’t know how the Darksaber ended up with Moff Gideon from Bo Katan.