With MAME 2003 Plus on RetroArch for Mac, how do I access the MAME menu? After having loaded MAME 2003 Plus’ core (e498229), Quick menu > Options returns “No core options available”. Supposedly I need to set the input method to mame_keyboard there in order to be able to access the MAME menu and I found no other way to do so.
Try entering the Quick Menu once you have actually loaded a romset. I don’t think MAME 2003-Plus supports using the Quick Menu when the core is started without any content.
(Once the Quick Menu is visible, you will see at that point you can activate the MAME menu directly from the RA Quick Menu without even needing to turn on the legacy keyboard mode.)