The dot at the beginning of a directory name will be hidden by default on a Linux box I believe. (" . es" would be hidden. "es" would not.) That may help you track down more files.

Change the default resolution to 1080p, 4k will be too much for the Pi. Add to your config.txt file:

hdmi_group=1 hdmi_mode=16

@mitu Thank you, I'll check that path first and then I'll check on the image producer.

@rogeriol Please open a new topic and add the info requested in https://retropie.org.uk/forum/topic/3/read-this-first, don't bump old topics.

@Azurden I believe you are confusing various uses of the word 'set' and incorrectly equating them. You need ROMs that match your emulator's needs. The easiest way to deal with this is to get yourself a complete collection (a rom set) of MAME 0.78 roms. Individual games are comprised of rom sets as well. Different versions of a game will have different roms comprising them. Missile Command set 1 and set 2 are two different hardware versions of Missile Command.
Get yourself a full collection mame 0.78, copy the games you want over to the roms/arcade folder on your pi, and then use lr-mame2003 as your emulator on the Pi.