All the Information I have so far found on the 2019 MY C63s Coupe, which is limited to press & Youtube release, leave’s a question I can’t find an answer too.....
The New York show release car & all other videos & reviews only refer to the 19” wheels being available.
Has anyone seen or heard a build option for 19/20” wheels ?

Yes, it’s an option

I like the RXC 19/20” option on the white cars. It was extensively used in launch of the vehicle, as is was advertised as aerodynamically developed for the car....
Hovever I still prefer the 767 option of 19/20”, which I picked for my black car.