How do you update faces on Photo?

For Catalina 10.15.7: 1) If you close photos and leave the computer on, it starts updating photos automatically while idle whether Photos is open or not. If you want to confirm it's happening, leave the Activity Monitor app open. It appears to use about 30% of CPU while idle. 2) In energy saver, I set the computer sleep to NEVER and left it on all night and logged in with only Activity Monitor ON and in the morning a lot had been processed 3) In Photos/People, per person, in addition to the banner prompt to confirm at top, I also use the link at bottom of each person page title "Confirm Additional Pictures". My gap appears to have narrowed significantly, but it seems the computer needs to make a few passes as you clarify who is who. I will post here if I find something unexpected. Seems to be resolving itself.

Whenever it is open but not being used. Just have it open whenever you are using your mac - however it can take weeks.