I am trying to understand why my question has been closed as too broad. My question was:
I did, of course, my research and I could not find a clear answer to this specific question. My expected answer was either yes It's a firmware limitation (like the one that I've received https://electronics.stackexchange.com/a/441516/33847) or no it depends also on the design with explanations of course.
I think only electrical engineers can answer to this question. I've received quite good answers even though I'm not sure are right because I've some thoughts that the capabilities depend on the location of the image buffer (i.e. if it's the camera buffer is before or after image processing). How can I clear my doubts? Should I post another question in a more explicit way? or is there a way to edit my question so I get another opinion? Do you have any pieces of advice?
After days of researches, I finally found a possible answer to my question. I'll report it here:
No, is not only a firmware limitation. According to this site there are cases in which the possibility of storing RAW images into the camera memory is dictated by the location of the image buffer. In cheap cameras the image buffer is often located after the image processing processor doing so the image is first compressed and then stored in the image buffer. Doing so you can use smaller image buffer but you can't in any way save RAW data to the memory.
This was exactly a possible answer I was looking for, (Even the one I received where okay for me but they were wrong) the proof that in some cases there are hardware limitations in storing the RAW image and there's no way you can unlock this feature changing the firmware.