Yes, it's the backend support--so (for example) if you go to Aurora and search for "nostr" you'll see the clients - and many (most?) of them say "requires GSF" (Google Services Framework).

Now some apps may say they require GSF but run fine without. For others, no so...

And while you can install Google services on Graphene in a sandbox I'd prefer not to...and (of course) there are other permissions as well.

So--looking for recommendations 😃 (i.e. "stand on the shoulders of others" as it were)