Configure Android Data Saver to limit background mobile data, then allow the few essential apps that need to keep working away from Wi-Fi.
Understand what Data Saver changes
Data Saver generally lets most apps use background data only over Wi-Fi. Apps you are actively using can still consume mobile data. It is therefore not a complete block on cellular usage.
Enable it on a Pixel-style interface
Open Settings > Network & internet > Data Saver and turn it on. On other Android phones, use Settings search or the manufacturer’s instructions because menus differ.
Make essential exceptions
Within Data Saver, open Unrestricted data and select the apps that need background cellular access. Google notes that some apps and services may not work as expected without it. Keep the exception list focused on real needs.
Test one ordinary day
Our suggestion: enable the feature on a day when you can check the result easily. Watch whether the apps you rely on continue to behave as expected while away from Wi-Fi. If one needs an exception, add that app rather than immediately disabling the feature for everything.
Think about why an app needs timely background access. A work communication tool may have a different role from an app you open only for occasional browsing. The right list depends on your responsibilities and how you use the phone.
Keep active usage in perspective
If your main data use comes from activities you deliberately start, background restrictions may not solve the whole problem. Review your habits alongside the settings. Consider doing large downloads when a suitable Wi-Fi connection is available and keeping a record of what changed during your test.
Review instead of guessing
Compare a similar period before and after the change, and remember that different activities produce different totals. Do not judge the setting from one unusually busy day. If a manufacturer labels the feature differently, verify its description before assuming it behaves exactly like the Pixel implementation described here.
Source: Official support documentation. Interface labels may vary with software version and device.