How to restrict background apps?

There is no option to restrict background apps data usage in a single go..you have to do it individually
or
use samsung max(but again personal choice)

You can put the apps which you don't want to run in background to the list of sleeping apps.

Follow the below steps to do it:-

1.Go to Settings》Device care》Battery》App Power Management》 Sleeping apps
2. Add the apps to the sleeping apps list which you don't want to restrict to run in background .

Also turn off background data usage for every app installed in your phone. For doing it perform thr below steps:-
1. Go to Settings》Apps
2. Click on an app for which you want to turn off background data usage.
3.Click on mobile data.
4. Toggle off "Allow background data usage".

In the same way press back button go to battery section and toggle off " Allow background activity" for the app which you want to restrict.

If it helps you. Click on three dots on the right side of my comment and click on accept as solution.

Also go to Settings》Notifications and turn off Notification for the apps for which you don't want to get Notification.