The Data saver mode prevents the data connection for apps running in the background. apps can also be selected for the "Data saver" function that are still allowed to use data in the background despite the active data saving mode.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Connections
Step 3:  Tap on  Data usage
Step 4:  Tap on  Data saver
Step 5:  Enable or disable  Data saver
  1. Open the Settings
  2. Tap on Connections
  3. Tap on Data usage
  4. Tap on Data saver
  5. Enable or disable Data saver

Samsung Instructions