Turbo Quattro

Signature FEC key 00060400

does anyone know how to calculate the signature for this key?

Кто-нибудь знает, как рассчитать подпись для этого ключа?

This is RSA signature.
You need private key to sign that.
To get that key from VW is simply impossible.
To try and guess the key is close to impossible, see here https://en.wikipedia.org/wiki/RSA_Factoring_Challenge
So in simple words - to create valid KEY for non patched unit - forget about it.