Same question from my side. I (only?) have ~8000 photos and ~250 videos, but it's running for several days already (with Photos either open or closed, with power on, and even with energy saving prevented in settings for a couple of nights.)
I do remember that Photos app crashed for me once, soon after upgrading to Catalina, but I don't know if that's related to this or not.
I also do remember that the analysis took a long time (but not >4 days like now) a year before, with Mojave upgrade.
For now I wish I knew about how much time I need to wait, or at least whether the process is actually doing anything and would eventually finish or is it stuck on some issue and it would remain analyzing forever? (Should I try to repair/rebuild the library?)