I've always been a bit confused about the right to repair debate, especially as it concerns John Deere equipment. I don't own any "new" John Deere products, but I do have a few pieces circa ~2010. Perhaps my experience is out of date.
Here's how it's always worked for me:
1. A code comes up on the computer.
2. A. The problem is self evident. Or;
2. B. I search online and find the problem. Or;
2. C. I search online and find the diagnostics manual, which I use to find the problem. Then I have diagnostics manual pdf forever, and can use this in the future.
3. A. I search online and find the parts diagram. Or;
3. B. I search my dealers website and find the parts diagram.
4. I order the part.
5. I install the part.
Has something changed with newer equipment that prevents farmers from doing this?
Newer Deere equipment has a lot of components that have to be adapted using DSA - turbo actuators, various hydraulic sensors, various suspension leveling sensors, fuel injectors, interior displays, and anything SCR related are the big ones. Basically, any sensor that needs a calibration step or triggers an emissions code, or a few intentionally vehicle locked modules (ECM).
Some newer equipment has no service manual available.
It's a subscription, with a DRM system so you have to use their app to browse the manual, and you can't print/save more than a couple pages per month.
The parts have to be unlocked with like a DRM system to work.
Fiddling around the way a casual working on their own car would isn't economically viable at scale. Labor use needs to be more efficient than that. Even if you can swap the right parts fast, lots of new stuff requires "permission" to install various hardware. Like some random make might not let you install a steering rack or something.
The parts talk to each other and verify each other's serial numbers and refuse to work if they don't match, and none of the documents you referenced exist.