Hi @Simba2, sorry to hear about this.
Have you checked whether the notifications for Facebook is enabled or not? Find and tap Settings > Apps & notifications > App-info > Facebook > Notifications.
Another thing that you can try is to clear the data for the Facebook app. This will reset all settings for the app which might do the trick. Keep in mind though that this will also log you out from the Facebook app, so you have to log in again afterwards. Find and tap Settings > Apps & notifications > App-info > Facebook > Storage > Clear data > Tap "OK" > Restart the phone.
Try this and let me know how it goes!
