No, that is false. Usage of passkeys is strictly optional. Passkeys are not used on an iPhone for access to iCloud or the device itself nor have any bearing on other devices you may have directly. They are used in place of passwords for Apps and websites. You can still use the password to log into the app or website even when a passkey is enabled for it.
click here ➜ Use passkeys to sign in to apps and websites on iPhone - Apple Support
Passkeys, should not be confused with passcodes or passwords as they are different things.
Passcodes are short number sequences used to unlock the iPhone. Passwords are longer alphanumeric sequences used to unlock the iPhone. Neither passcodes not passwords used to unlock the iPhone have any relation to iCloud at all.
You can choose to not use a password or Touch ID on an iPhone and keep it entirely unlocked. This again has no relation to using iCloud.
You can use a passcode or password to keep it locked but not use Touch ID.
If you use Touch ID, a password or passcode is required.
iCloud relies on your Apple ID and its password which is unrelated to your iPhone's unlock passcode or password or any passkeys you may have created.
You can choose not use any of the iCloud features by turning them off in Settings.
