Hello!
Around the time of the release of version 1.11.0 in May, I updated the game to the then current version of a widely used community sourced database of joysticks and gamepads:
https://github.com/mdqinc/SDL_GameControllerDB
So everything in there (at the time) should work, assuming it was registered correctly. Even if not there, I can and have assisted people with workarounds on how to supply similar info to MULE Online locally prior to runtime. Even without such conditions, the game engine used will attempt to do its best with the cooperation of the OS and device drivers to use the device as-is, defaulting the button order to their default. In which case, on a joystick with a very limited number of buttons *might* experience issues not being able to bring up the game's main menu or dashboard during the game. For that unlikely case, I'd recommend having a keyboard attached and at the ready.
But alas, I know of one person who's reported they have successfully used the SPEEDLINK SL-650212-BKRD Competition PRO EXTRA USB Joystick.