Hi,
I'm also fighting and trying to understand how to get MAME up & running in LibreELEC.
After tried the complex ways (Advanced Mame Launcher),and so on, I'm trying the first "Hello, world!" test
1) Installed the Arcade (MAME 2003) add-on from the add-ons menu
It install a shared library game.libretro.mame2003.so in /storage/.kodi/addons/game.libretro.mame2003
No mame executable (or I'm not able to find it)
2) In main menu, Games, I select "Add games", and add the folder where I have copied the roms (in my case /storage/games/mame/roms)
3) In same menu (main/Games) I pick the recently added folder, and pick a zip file.
ERROR: But instead of opening in MAME; it simply open the zip file to show me the inner content (the bin files)
Of course, if I try to open a bin file, it fails because try to open with other emulator (no mame)
I imagine it a silly misconfiguration, but I'm not able to find any place to say "the zip files are open with MAME"