Note that it isn’t a lost cause with nostr. Just opening a client, scrolling and closing won’t reveal “Last seen”, it is the moment you interact with nostr that you reveal that information. This means when you post something, or like a post, it is revealed, but I think people expect that. Where there can be improvement is with other actions, like adding a bookmark or adding a mute, people don’t expect this to be a public action, but many clients store this in a list signed with your pubkey so it reveals your Last seen.