The Neo Geo BIOS determines the region (Japanese, US, European) and the mode (Arcade MVS or Home Console AES). If you want to play the "Home" version of a game (which often has an options menu and limited continues), you must change the "Neo Geo Mode" setting inside the RetroArch Quick Menu while the core is loaded.
Today, RetroArch is widely considered the best way to experience these games on modern hardware. However, Neo Geo emulation is unique because of its "BIOS" requirement. Unlike a standard SNES or Genesis ROM, Neo Geo games require specific system files to function. neo geo roms for retroarch