I don't think this is how it works. I set up a site association so any time iOS sees a https://damus.io/{npub,note}* click it should pass it to a handler within damus. Why some links don't obey this is still a mystery to me.
Ohhh I totally misunderstood, I thought this was about URL previews. For deep links I’ve noticed iOS can just be a pedantic about where you’re clicking the link. What usually works for me, at least when testing, is pasting the link in Notes then tapping it from there.
For example: http://i.ii.md/8eGqsZcEGT.mov