@retropieuser555 that's absolutely brilliant - thank you so much!
It appears that the original installation was done in Linux for some reason, so at least this way I can have a fiddle around and try to learn how it all works :)
@bigbay you are welcomed.
If you need any help creating your own image feel free to ask here.
There are resources and options to build a gernan based image.
I.e. you are even able to set some arcade games from Atari and Capcom (Dungeons and Dragons, Aliens vs. Predator, Xybots,...) to german language.
Get ready for "Münze einwerfen!" :D ("insert coin!")
Is this something I can update on there, make a new backup image, and flash to my newer pi?
Update your system from the RetroPie-Setup on the old system - say yes when asked to update the included kernel and OS packages - then transfer again a backup to the new system.
@fullauto2009 An upgrade in place is not recommended, as it's not supported even by Raspbian. Note that attractmode is not compatible yet with the Pi4.
If you want to set up a new model, simply clone your /home/pi/RetroPie folder to your PC, install RetroPie on the new SD card, delete the new /home/pi/RetroPie folder, replacing it with the existing one.