When I run a Neo Geo rom from either GnGeo or FB Alpha, I get the “Press Start” text and insert coins. Then, once the game starts I get, for example, Metal Slug ammo info and lives. Also full sound. But no game sprites or background layers. I’m fairly experienced in emulators and ROMs on Mac and Windows machines so I’m aware of the usual, i.e. Bios rom and unzipping it or not. But never on Linux. So this just seems to be a settings problem. Maybe?
Also, CPS2 ROMs work fine in FB Alpha. Does the Pi version not play NG?
I had the same issue, but it was only with a few games in FBA. The solution was to download the rom from a different source. In particular I remember in King of the Monsters the main character sprite was invisible, but everything else was there. Downloading a different copy of the rom fixed the problem. Overall, I’ve found the mame and fba emulators on the pi to be extremely finicky. I’ve had to do a lot of downloading multiple copies of a rom to see what works best.