Comment 9 for bug 1989976

For macOS specifically, Apple has a restricted entitlement that grants full access to the system AuthenticationServices framework, which includes both physical security keys and passkeys via iCloud Keychain. There's some information and a link to apply for the entitlement at https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_developer_web-browser_public-key-credential.