@KMFDManic Once done the trick of double compression, retroarch doesn't detect the nestopia core arguing it in the command line.
Por example:
/bin/nes /usr/share/games/nes/kachikachi/CLV-Z-CAYIC/CLV-H-ABZZG.7z --retroarch --core nestopia
--retroarch --core nestopia or --retroarch --nestopia...