Ah, well! That’s what I call very playable. I think it’s just the shadows that are in Kokiri forest that are graphically stupid. Once you’re out of there, it’s all good. Eg, the first dungeon basically plays flawlessly. So yes! That’s how it is basically is my response!
As for making the icon, mupen64plus isn’t actually in the cores folder, since it’s not a core that’s used with retroarch.
Here’s what you can use though: (change the name to your rom file name obviously)
mupen64plus --resolution 320x240 --fullscreen /home/cpi/games/mupen64/zelda_oot.n64