How to dismiss every notification except from your messaging apps

Steps

1. Open Settings > Notifications > Dismiss Notifications and choose Dismiss if logged.
2. Tap Exclusion list.
3. Tick your messaging apps (use the app list to find them).
4. Go back. Everything is dismissed except the apps you ticked.

Alternative

If you only want to clear a few noisy apps, choose Dismiss only selected apps and add just those apps to the Inclusion list.