I think the confusion is that you can restrict if an app can be used at all, so then it will not appear in Screen Time. That is not what you are attempting to accomplish by not showing the Waze/Maps or Baby Monitor app that you are currently using.
Even though you are not looking at the screen, they are currently running, so their use is being recorded in Screen Time. You cannot exclude apps from reporting their usage, you can only prevent an app from being used.
Another example would be for listening to Music, where it would report how much time is spent listening to Music, not just when you are looking on the screen.
You can send feedback to Apple here if you think there should be an option to exclude it's reporting to Screen Time while it is currently running on your phone.
Product Feedback - Apple