SpiralDJ

This forum explains the problem and provides a solution. https://melonds.kuribo64.net/board/thread.php?id=1143 It was an issue with flatpak "MelonDS adds the user home directory as a filesystem that it can access and open files from by default. It can access files outside of that it seems, but it has to mount them separately first. What I've done is to add my nds directory as a filesystem to the melonDS flatpak using Flatseal. I can now load my games via Steam just by adding the filepath as an argument in Steam Rom Manager and the file is no longer mounted to open it." - sverth_blaed from the melonds forum