Ditto implements the full Mastodon API which allows interoperability for any Mastodon client (like Tusky, for example), and we're continuing to improve the Mostr Bridge (npub1d03…pzfs) for communication across protocols. However, we've moved away from implementing direct ActivityPub support. We made this pivot so users of Ditto don't have to take on the burden of the clunky and insecure ActivityPub protocol when we realized that thanks to the bridge it wasn't necessary for cross-protocol communication.
Ditto is really about taking the good ideas from Mastodon and bringing them to Nostr. Most importantly, community servers.