There was a thread mentioning how to set up and configure it to run nicely here.
The problem is, you need go know how to build files, and although there were included instructions, a lot of people had hit or miss success. It’s something I did try to help a few people with, but without know exactly what they were typing, and what their specific configurations were, there was only so much I could do to help.
It was actually one of the main reason I made the aforementioned custom DEOT custom image. So basically, to get it running it can be tricky for some. You’ll need install dependencies, alter a configuration file, and edit an action file. On top of that, it runs way better once you update the Lima/Mesa files/drivers, in particular a lot of graphical glitches get resolved.
Playing games on the gameshell isn’t difficult. They mostly run fairly well, with a few hit or miss exceptions. Putting together the files can be difficult, or rather difficult to find all the information.
The custom image is there as a shortcut with everything required to play mupen smoothly installed, but I still strongly encourage people to try putting it together themselves, learning how to do things in the process.