Does Screen Time log apps running with no windows open or while in screensaver mode? I noticed my Mac is logging 10hr+ daily usage of Mail, Safari and stuff. But they are just running in the background - since I don't want to always quit and launch these frequently used apps. But I am not sure how exactly the Screen Time is calculated. 

Does it still accumulate when these apps running in the background, and even if I set my Mac to screensaver?
I have noticed that the Catalina version of the app simply displays how long apps are open, rather than how long they’re being used.

So if I keep Safari open on my Mac all the time, it reports that duration – even if Safari is in the background while I’m doing other things. 

If I put my Mac to sleep with Safari frontmost, when I wake it up, it will be counted as a pickup. On iOS, this makes sense because when you wake up your iOS device, you are on the home screen, so you have to actively choose which app you are going to use. Also, it doesn’t seem to be reliably updated on the Mac; right now, I’ve put my Mac to sleep a couple of times yet when I awaken it, it doesn’t add to the number of pickups. And it’s not counting the System Preferences app, which I’ve used several times after waking up my Mac to view Screen Time.

So, in my opinion, the Screen Time report doesn't make proper sense in macOS.