With no experience with deere tractors, I can't say if there is a display that you can access the codes.
I deal with many engines at work. I have the option of getting a diesel laptop, but decided to hold off for our location.
At $6000.00 for the laptop loaded with all the different brand oem software. Then the annual licensing fees. Well.... you get the picture.
All my equipment at work has a display that will give me the codes. The exception is our Doosan forklift. The forklift will give you the codes with a little persuasion, and looking up how to do it online. Then it's a matter of counting blinks of a light to get the code
I can handle most repairs by just looking up the codes. And Google is my best friend with this. Punch the code into the search bar, and it will tell me what it is. And depending on the forum I can get a pretty good idea of the fix as well.
The only time software is needed is programming injectors, ECM's, or calibrating something such as an EGR valve. It's also handy trying to determine which sensor is causing an issue if the code happens to be something where it's a calculation of multiple sensors. This last part isn't a deal breaker though since it's usually just a calculation between a couple sensors. So if one is bad, they usually recommend replacing both.
Laptop does have some handy diagnostics abilities. But this is used to determine a faulty fuel injector or something similar. But if your running those tests, then it's not a simple fix and your probably gonna be looking at some major down time anyway.
ECM can be programmed on the bench. Just provide the engine serial number and they can update payloads and set it up before being shipped.
I handle all the easy stuff at work without the software. I might have to get a dealer involved a few times a year. This is a fleet of 300 plus pieces of equipment.
Did I mention Google??? You can get diagrams, so if your hunting for a sensor, it can get you really darn close.