I saved pub key as username on iCloud Keychain. Auto-fill expects a second field to appear for password. Why is even possible to "log-in" with just the pub key? Another issue now I can see my private messages but not the answer to them.
Discussion
Pubkey login can be used for viewing nostr from someone else's perspective, or viewing your feed or notifications even from a device where you don't have the private key. Good to know about the auto-fill!