Setting up a Passkey for your Google login will not prevent you from using YouTube on your Apple TV.
Here’s Why:
Passkey Basics: Passkeys are a secure, passwordless way to log in to accounts on supported devices, but they don’t replace traditional sign-in methods.
Apple TV Compatibility: If Apple TV doesn’t support Passkeys, you can still log in to YouTube using your Google account with a traditional password or a linked device.
So, you’ll still be able to sign in to YouTube on your Apple TV, even after enabling Passkeys for your computer.