I am over two YEARS and still at 0 scanned faces. Apple really does not care. They are not at all interested in fixing things that break. It's too hard. They simply must stop touting it as a feature, because it simply does not exist anymore.
I had this same problem even after I upgrade iphones to the 13.
I would try this first which doesn't require deleting anything.
I didn't bother with the last sugguestion to use a 3rd party software to repair you ios. As a commenter sugguested you can just use iTunes to repair your iOS if you really think thats the problem.
The best take away from the video was going into Settings >Photos > Reset People Suggestions.
I would try this first and plugging it in overnight and seeing if it worked before trying the next fix I found.
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What I think actually worked for me was following this persons advice and plugging it in over night. I would suggest backing up your iphone before trying it. I didn't and was so mad when it didn't seem like it was working and I deleted all the named people I already had saved and the phone was recognizing. Bewared though as of 1 day into the "fix" all the photos were scanned but some of my previously recognized people didn't populate. However there is hope since the iphone does say on the bottom of the People folder "Updating People... To finish updating your people, lock your iPhone and connect it to power." It might still be combing through the photos for lesser photographed people which may take more time since they aren't as frequently photographed.
FYI my iPhone did not ask "if you want to restart the faces scan" my People folder still had the same message screen "0 Photos Scanned" "To finish scanning your remaining XXXXX photos, lock your iPhone and connect it to power." which made it seem like I did nothing to correct the issue.
discussions.apple.com
<You may have a photo or video on the iPhone, that cannot be processed and needs deleting. But that kind of error is very hard to track down.
Or the people database is corrupted. Then it would help to reset the people database and start over. To do that you would have to delete all named persons from the People album. Photos will then ask, if you want to restart the faces scan.
Or wait for the next update to iOS to see if a bug fix will take care of this problem.>
Hope this helps someone else with this incredibly frustrating issue