This usually happens when a passkey is created on another device and the passkey has not been synced or has been transferred to the device that you are actively using.
Some example scenarios and issues that users experience:
Your passkey was created on another device using iCloud Keychain on an iPhone or Mac but you have not synced your iCloud with your Windows computer
The iCloud for Windows app is installed but not properly configured for password/passkey sync
You have not signed on with the same Apple ID that has the passkey within your iCloud Keychain on your Windows device
Your iCloud Keychain sync settings on your iPhone and or Mac are not enabled
The Windows computer does not have the latest iCloud for Windows update that supports passkeys
The operating system you are running may need to be updated to a version that supports passkeys
The browser you may be using does not support passkeys
The device's biometric authentication (fingerprint/Face ID) is disabled or not set up
Steps to resolve these issues:
Install or update iCloud for Windows
Sign in with the same Apple ID that you used for creating the passkey on your iPhone and or Mac
Enable password and passkey sync in iCloud for Windows settings
Make sure iCloud Keychain is enabled on your iPhone and or Mac under Settings > [Your Name] > iCloud
Use a supported browser on Windows (Chrome, Edge, or Safari)
Restart your browser after setting up iCloud for Windows
The syncing process might take a few minutes after setting up iCloud for Windows. If your passkey still doesn't appear, try signing out and back into iCloud for Windows, or restart your computer.
Update the operating system of your device
Try to use one of the following browsers and make sure that they are updated to the latest version:
Chrome
Safari
Brave
Firefox
Enable and or setup the device's biometric authentication methods