Samsung
Turn Data Saver On or Off auf Samsung
Data saver limits mobile data for apps that are not currently open on screen. Once it is active, apps in the background cannot send or receive data unless they are added to the allow list. This is why chat apps, mail clients or cloud backups sometimes stop updating until you open them manually.
The setting sits in the connection settings of your phone, separate from Wi-Fi controls. Turning it on affects mobile data only; Wi-Fi connections keep working normally for background apps.
Where to find Data saver
Open Tap on Settings ➔ Tap on Connections ➔ Tap on Data usage ➔ Tap on Data saver, then use the switch to Turn On/Off Data saver.
While inside this menu, you can also pick which apps stay exempt. Tap the option to allow specific apps while Data saver is on, then enable the toggle next to each app that should keep working in the background, such as a messenger or navigation app.
If background sync feels unreliable even with Data saver turned off, check battery optimization settings instead, since that is a separate system feature with its own restrictions.