I made my handbrake and it works via USB on pc, I don’t know how the fanatec handbrake connects, but so far it seems like wheels are registered as a controller on FM7, when I’m on mine it shows all the keybindings as keyboard keys.
I just got word back from the official Fanatac support and they say that FM7 as well as all the other Forzas don’t support analog handbrakes on the xbox which is why it is “highly unlikely that T10 will implement the support in the future”.