It's probably a translation problem. I previously asked titled speedrunners, none of them know exactly how this function should work. The fact is that different emulators and their versions implement the "left plus right" prohibition function in different ways.

In one case, both keys stop responding, and in the other, only one continues to work. There is no information which emulator would be more accurate, for example, Nestopia or Mesen.

I'm not answering an old question, but asking for help, this is relevant now.

Can I clarify which is correct? When pressing the left while the right key is pressed, does the movement to the right stop or continue?