By default there’s no way to hotlink, if you will, to a post on any platform. Now some apps might be doing something special to get around this, but out of the box this isn’t supported at the moment.
Now there is an issue on lemmy itself which I’m exploring that should “fix” this: https://github.com/LemmyNet/lemmy/issues/2987
But I’m not sure how that might translate in a mobile app.
Correct. As I can only provide links to posts that are on your selected home instance. Eventually I’ll change this but you’ll get a 404 page for links that aren’t on your home instance, but see my P.S. below.
P.s. there have been changes to the Lemmy API that have prevented me from getting updates for about a month now. So most of the results you’re seeing are from old posts only. Until I can rebuild the crawler or find a new API there won’t be any new content.