How to get an overview of which app are allowed to background data for Android 7
Not sure about GUI interface you want or a third party app that may do this for you, you can use CLI (terminal app or adb shell):

~$ dumpsys netpolicy | grep '^[ ]*UID=.*METERED_BACKGROUND'
  UID=10173 policy=4 (ALLOW_METERED_BACKGROUND)
  UID=10176 policy=1 (REJECT_METERED_BACKGROUND)


File /data/system/netpolicy.xml can also be read directly with root access.

~# awk '$2==10173 || $2==10176 {print $2,$1}' /data/system/packages.list
10173 com.whatsapp
10176 com.simplemobiletools.gallery.pro


Or:

~$ pm list packages -U | sed 's/package://; s/uid://' | grep -E '10173$|10176$'
com.whatsapp 10173
com.simplemobiletools.gallery.pro 10176


It shows that WhatsApp has Unrestricted data usage allowed, while Gallery app is denied Background data usage at all. Rest of the apps have default behavior i.e. they can use background data but not in Data Saver mode.

You can do some further scripting with aapt tool to get e.g. app label / name.