I assumed the arcade folder was for putting Mame roms in, but the Wiki says to put them in the folder for the individual mame emulators. What’s the “arcade” folder for? https://github.com/retropie/RetroPie-Setup/wiki/MAME
I need to update the wiki for 3.5 with the arcade stuff. And it’s possible there are some config issues with a couple of the arcade emulators for the arcade folder. Would be interested in any issued you encounter so they can be fixed.
There are some config issues with mame/advmame as they look for roms in the other location – this was overlooked when arcade was added. Need to think of a solution for those.