Solved the black screen problem : we must put the neogeo or other console bios zip inside the rom folder, next all will works fine, tested with metal slug 2
for sure you have to put the roms inside "sdcard - switch - pfba - roms" and the roms must be ziped so dont unzip them.... I have tryed to download some samples from 2.97.42 fba romset but always black screen.... if someone have a good repository share it