Passkeys are stored on the device where they are created. To make sure your passkey ends up in the right place:
Windows PC
You must have Windows Hello or a password manager that supports passkeys (RoboForm, 1Password, Dashlane, Keeper, Bitwarden).
Mac (macOS)
Use Safari (not Chrome or Firefox). Make sure you're signed into your Apple ID and that iCloud Keychain is enabled. Touch ID will be used to confirm the passkey.
iPhone / iPad
Open this page directly on your iPhone or iPad to create a passkey there. Scanning a QR code does not work for passkey creation.
Android
Open this page on your Android device to create the passkey there.