Tagging people isn't really search in most apps, maybe nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z could comment.

Search for old conversations is hard, unless you remember some very specific words being used - your searching is anonymous, we don't personalize it in any way to prioritise content closer to you. A filter by author could help, but the app would need new UI for that.