People will finish updating when Photos is in the background

Using macOS 10.13 High Sierra and iOS 11, the People Albums now sync which is great. But Photos > People reports "People will finish updating when Photos is in the background" to me even since the official release of macOS High Sierra.

I have a few questions:

1. What is "in the background"? Is the app Photos open but minimised or at least not the active application? Or should you close the app Photos?
2. How can I see any progress?
3. Can I devote more resources to speed up the progress? Like involve iOS devices connected to the same iCloud account? If iOS devices can help, question 1 and 2 apply for those as well 🙂

I read about a process called photoanalysisd but the information regards macOS 10.12 Sierra:

https://blog.yimingliu.com/2016/09/20/check-progress-of-photoanalysisd/

I asked Apple Support how I can see progress and what I can do to speed things up. Maybe keep a machine active (for instance the app Double Shot prevents your Mac to go to sleep) or involve iOS devices connected to the same iCloud account.

They came up with three answers, during the same conversation, only regarding getting progress in scanning:

1. Keep the Apple Photos app open on macOS. Otherwise it won't scan.
2. Close the Apple Photos app on macOS. Otherwise it won't scan.
3. Don't bother keeping your macOS device involved if you have iCloud as iCloud takes care of the scanning.

They finally stuck with the second answer after talking with each other but they don't really know.