Does this mean that you have to quit Photos, or that you can't quit it?
"Photos will continue scanning your remaining 82,337 photos when you're not using the app and your Mac is connected to power."
Question marked as
You should be fine to quit the Photos app. If for some reason after a long time the photos aren't done scanning, you could try minimizing the photos app while you continue to work on your Mac, but it should be fine if you quit.
