@muscov
Could Vivaldi not detect that it doesn't have permission to use passkeys, and warn the user?
We ask for permission to store passkeys and use iCloud passkeys, but in this case the dialog is not shown. I cannot tell why, but it's the same case as other chromium based browsers, including Chrome.
It seems strange that a second device needs to be involved. This isn't the case with Safari.
I agree, however, on other websites the passkeys are working as expected - seems like account.apple.com is a special case.
Could Vivaldi use the macOS ScreenCaptureKit, or similar technology, to read the QR code? 1Password does something similar to this.
I don't see the reason why we would do such thing, as authentication must happen on iOS device and passkeys are handled by the OS.