These are regulations, not laws, and can be changed fairly easily. E.g the EPA recently changed the rules requiring NOx sensors and power downs, which were the most failure prone components of the system, while still mandating the actual equipment that scrubs NOx.

There's no particular reason why a mechanical device needs computers for emissions, as the emissions removing components can still be attached and managed via simpler means. All emissions removing components are effectively physical devices, whether you are talking about carbon filters or PCV valves or particulate filters or the urea fluids that are added to the fuel. None of them requires complex software in order to function. There is no reason why you need to buy an official John Deere branded emissions component that is software locked to tractor and costs 10x the price of third party components that do the same thing.

Also, there is a large room to maneuver between "I want a sensor with some circuitry in it" and "the entire tractor is a proprietary computer with locked down parts". The right to repair movement is not about removing tech, but removing unnecessary proprietary tech that is designed to prevent owners of devices from repairing those devices themselves or with third party components.