The best option is a temporary phone number germany to deflect suspicion and make yourself a foreign user. I don't like to leave my number in such cases. So you should also consider whether it's worth registering personal details on the internet at all.
If your account is blocked, you will not be able to unblock it via Yubikey. It is better to leave your phone number. Although I would not take any chances, because the number is linked to the service and your account may be displayed there.