Deep/universal links have not worked on twitter for years. I think this is by design to keep you inside the app - opens inapp web browser instead.
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.
Discussion
This is a good point. I think you might not take Twitter as a reference for your tests. I usually test deeplinks / universal links from Notes