A cantilever brake?
I find the current trend of reducing tire clearance by 5mm to 7mm on gravel bikes and calling them "all-road" bikes amusing. We're basically back to the same thing that they called a gravel bike in 2016. Meanwhile "endurance" road bikes are coming from the other direction, and shipping with 40mm of clearance, and at least one team is riding Factor gravel bikes at Paris-Roubaix (albeit setup with 28mm tires).