[watermelon0]

This depends on the implementation.

If you are in Apple world, your keys are synced between iOS and macOS (and saved in Secure Enclave, so you need TouchID/FaceID to complete flow.) In 'Google' world, you can use them between Android devices and Chrome browser.

However, if you access from unsupported app/device (e.g. use Apple Passkeys and want to access from browser on Linux machine), you can always just scan QR code with phone, and use it to log-in.

You can try it on https://www.passkeys.io

[meirwah]

you can try here too https://passkeys.guru/