There should be no Push notifications on nostr. Because push means there has to be some backend that uses google firebase cloud messaging or similar for sending the push notifications to your device when some conditions are met. And that means you've just introduced a centralized component in your application that is supposed to use a decentralized protocol. See the problem? The only way to be a trully decentralized client for nostr is not to use push but pull in a background service that you try as much as possible to not be killed by the system and use as little network and battery as you're able to code it. It might seem uncomfortable because you're so used to have pushs with apparently no cost to you. But there's no such thing as a free lunch. The third-party risk is there. If you want freedom tech that is trully independent of centralized clouds and backends you need to accept the cost.