I looked at the nostr protocol, I don't understand how it can efficiently support likes and comments from strangers.

because everything is modeled as an event. And a client only pulls events from peers that it follows.

on one side, a viral post will attract lots of like events. on another side, how can a client efficiently gather all these events from relays, accumulate them, and store them?

Damus is a nostr client for iOS that was just released on the app store

https://apps.apple.com/us/app/damus/id1628663131

What about Android users?