Not sure how you imagine push notifications to work, but literally Google provide a "service" for this so app developers don't have to. https://en.wikipedia.org/wiki/Firebase_Cloud_Messaging

So that there's only one network connection delivering all the messages to apps, instead of 1,548 SSE/WS/XHR/GET(!) connections all ricocheting around and timing out and getting reconnected and sending 200MB of pings every minute.