You clearly did not check at all.
Pubky does not work like Nostr.
Nostr signs every message with the identity key. Pubky signs PKARR to publish identity + endpoints, then uses revocable sessions to authenticate to any homeserver/app.
PKARR updates can be signed offline. The Pubky app is local-first. Network is for syncing/publishing, not for producing signatures.
So comparing Amber offline signing to Pubky is mixing layers, and a misunderstanding of the design.