Thanks for the video.

My Pi did not have a gngeorc file in the ~/pi/.gngeo/ dir (which is actually a symlink to /opt/retropie/configs/neogeo). I created gngeorc in the mentionend dir and filled it w/ these settings:

p1control A=J0B0,B=J0B1,C=J0B2,D=J0B3,START=J0B9,COIN=J0B8,UP=J0a1,DOWN=J0a1,LEFT=J0A0,RIGHT=J0A0,MENU=J0B7

(see this link for an example gngeorc file)

And now it works. One can switch to “home mode” instead of arcade mode (the game then lets you save games on an emulated memory card then). By adding the following line to said file:

# system type? arcade or home
system home

[edit] If I choose Home Mode then some graphics are garbled…