Carbon is the ideal material for this purpose if designed properly. If a reputable manufacturer says it can hold a rack then I would not hesitate to add a rack and load the MF up.
The first bike that came to my mind was the trek 1120, which is not a gravel bike but an off-road touring/adventure bike, but with a carbon frame and racks designed for that frame. Totally not what you were looking for but I think it's cool.
https://www.trekbikes.com/ca/en_CA/b.../1120/p/22005/