Are you using the new Damus TestFlight version?
Discussion
using nostr:npub1n0stur7q092gyverzc2wfc00e8egkrdnnqq3alhv7p072u89m5es5mk6h0 test flight, if you want to post gif from giphy just copy paste the link but delete the "?" til the end of the link, it will show up normal
My Damus don’t work in my iPhone