What should be whitelisted in a firewall to allow push-notifications?

I'm using a firewall (NoRoot) on (Samsung) Android (10) to try to harden it, but now, push-notifications aren't coming through. I'm trying to figure out which apps/services are responsible for that and what URLs/ports need to be whitelisted. I've seen several candidates that might be it: * System * A *different* System‽ * System (Uninstalled) 🤨 * Google Play services/Google Services Framework * AASAservice, Accessibility, … … …, Wallpapers, WlanTest (very long list) * Hiya Service Most search results just mention this page which doesn't specify the app/service that requires the URLs and ports listed. Likewise, this answer (which is outdated since GCM is deprecated) also doesn't specify *which service* to whitelist. And this page outright recommends just allowing everything which defeats the whole point to a firewall.