Why is there a loading bar at the bottom of the main page fo Photos app after installing macOS Catalina?

Ever since I upgraded my iMac to macOS Catalina, there's been a loading bar that appears on the default page of the Photos app. It says things like "Detecting Duplicates", "Curating Best Photos", "Analyzing Scenes", and "Analyzing Favorites". And yet, despite this, the loading bar hasn't even filled in completely and it's been several hours. It's still at that the same spot it was. What does this loading bar mean, what is it doing, and how do I fix it so it completes the process and goes away?