I never post here, but I'm writing this in hopes that I can help a brudda out that's still struggling with the Joiplay black screen issue. I'm running my game on version 18 with the patch, and I somehow actually fixed the missing textures. I can't say EXACTLY how I did it, since I was mashing random options out of frustration and it worked so I never looked back. Basically, make sure your game is 1024px wide in the Joiplay RPG settings. then, start ticking on every option you can find such as vsync, frame rerendering and whatnot, one of them (or perhaps a combination of them?) should fix your game. Imma head out n enjoy the game now, cheers
edit: I went ahead and narrowed down the culprits. Try disabling Path Cache in the Joiplay RPG settings and enabling Prebuilt Path Cache. If that doesn't work, try running the game with Path Cache enabled first. If on second boot it doesn't work anymore, disable it and have the prebuilt on. I suspect this is necessary because there are issues with loading assets on joiplay with this game.