I was browsing Wikipedia and humans on Earth know a LOT more than I expected on the galaxies in our universe. We know how many there are, which ones are the oldest, the furthest, the largest, the smallest etc. Now we haven’t even ventured further than our moon. In the Star Wars galaxy, do astronomers know basically all the details of the other galaxies based on observation even though they may not be able to get to travel to them?
The Star wars galaxy seems to have a few "companion galaxies", that are pretty close. That can be reached via Hyperspace.
All the farther galaxies? They are unreachable! Unless there is a extragalactic Invasion coming, nothing of value happens regarding them: https://starwars.fandom.com/wiki/The_galaxy/Legends#Extragalactic_interaction
Extra-galactic travel was difficult due to a hyperspace disturbance beyond the edge of the galaxy that prevented hyperspace routes very far outside the disk, and beyond this, the barren vastness of the Intergalactic Void. However, by the time of the Clone Wars, contact had been established with the two small galaxies orbiting the galaxy: the Rishi Maze, also known as Companion Aurek, and Firefist, also known as Companion Besh. The InterGalactic Banking Clan had influence as far as these locations.
At the same time, if you were a adventurer, pioneer, scout or explorer there were the Outer Rim, Wild Space and the Unknown regions left for you to explore. Never mind some hard to navigate stuff like the Maw.
There was the Extragalactic Society, but even it cared mostly for the nearby galaxies.
It is improbable that nobody cared for the farther galaxies, but since you cannot reach them and they cannot reach you - there is only so much you can learn as opposed to all the stuff close to home worth exploring.