It asks to enable push notifs, then sends the push endpoint to server along with pubkey and relay, server monitors the pubkey on relay for unanswered nip46 messages, when detected sends a push to wake up the service worker.

Nwc flow is quite similar, so it should be possible to have the same thing there.

Server side is https://github.com/nostrband/noauthd - not a beautiful piece of code, but can be an inspiration.

You'll also need strfry or other relay that stores ephemeral events for a while so that woken up service worker could fetch them.