Push notifications is a core ability of the OS that cannot be turned off. If none of your apps have notifications enabled they will still get push notification

Push notifications is a core ability of the OS that cannot be turned off. If none of your apps have notifications enabled they will still get push notifications but just not raise an alert (kinda like what happens in Do Not Disturb mode). To completely disable notifications you would need to edit the mobile operating system to remove the code that establishes and maintains a connection with the Apple Push Notification System (APNS) or the Google equivalent. This is exactly what Graphene OS does: the Google push notification code was removed from the Android open source code base. Result: no push notifications and longer battery life (because there's not a process constantly staying in touch with a notification server).