There is a uri for opening links inside nostr apps, but the only place I've seen it is in Pokey, which is an android notifications client. Otherwise I just copy-paste the npub to another client. Sorry it's janky.

You mean a URI scheme? https://nostr-nips.com/nip-21

#asknostr

If you copy the npub and paste it in another client it should open that npub stream. As it is a npub you won’t be able to do much but if you copy then sec into another client you should be able to run that account on the other client.