Use Android Nougat’s "Data Saver" (Android 7.0+) under this site How to Restrict Background Data for Metered Wi-Fi Networks on Android mentions:
Android 7.0 Nougat introduced a much more granular way to take the reins on your mobile data with a new feature called Data Saver.
Basically, this allows you to limit background data used by apps, but whitelist anything that want to have unrestricted access. This means background data is disabled for every app by default, then you can pick and choose where to grant unlimited access
And that’s all there is to it. It’s worth keeping in mind that this only applies to mobile data-all apps will remain unrestricted while on Wi-Fi.
My question is whether this
Data Saver option applies to Wi-Fi that you set to metered, meaning metered WLAN?