You can use nostr by just installing an app, but you can also use it easier without even having to install an up, since there are plenty of web clients to chose from.  Do they need to be polished still?  Sure, they do, but so did the #BirdSite at the beginning, and judging by the speed they are improving, some might be much more usable than that soon.

Does SN have a nostr strategy?

eh until using nostr is as simple as installing an app there isn't any chance of it seeing real widespread adoption.  I've hardly seen any non apple users even mention it.