also, a lot of things in stuff like ROMs is about I/O to component in the devices, so you can disassemble and decompile all you want but without the right specifications and context you cannot say what the code does.

so it will also need all specifications of the hardware platform you are running the code on, as well as in this case perhaps even hardware in the catridge etc. (heard those also sometimes have their own chips etc...).

i'd say for 'regular application code' that runs within an OS it might be easier, but still you need to provide a lot of context from the actual execution environment to reason properly what the code actually does? (what does INT 80 run and possibly return anyway, that code is outside of your target binary)

There are several scientific publications on this. But I don't think the latest models are available as convenient plugins for IDA or Ghidra. Guessing variable and function names are considered as relatively easy nowadays. Types and structures are the challenges now.