Vertrag

Depends on if he can sell the car to someone other and at which price.

Some dealers like this deals, some not.

I think I also remember people offering their configuration in the forum here after the dealer said "No", trying to find someone who will step in and take their contract to shorten their own waiting time.
However, this was a rare occurence and I have no idea whether this ever had success, let alone on how to properly execute such a contract handover.

Transferring an order to a third party might not be accepted in case of a leasing. You can always ask your dealer.

Not a legal text, but a good summary of how it works:

https://www.finanztip.de/kaufrecht/lieferverzug-auto/#:~:text=Mahnung%20und%20Nachfrist%20setzen,Mail%20an%20den%20Händler%20senden.