How to make an Android smartphone actually go to sleep?

When I turn the screen off on an Android smartphone, I want battery life to be conserved. Thus, I don't want any third-party apps running in the background, and I don't want the device periodically turning on WiFi (or connecting via 2G/3G/4G/5G). I set up a test Android Samsung smartphone running Android Nougat, and installed just 25 popular apps. I set all 25 apps to "Always Sleeping" in Settings. I then let the device sit for 8 hours with the screen turned off. During those 8 hours, the Android device connected to a WiFi router 59 times and transmitted/received data each time. I don't want to turn on Airplane Mode, because I still want the device to be able to receive and log incoming phone calls. Is there a way to accomplish this with Android (on a non-rooted device)?