I've got this game to work. I've tested using Proton and I found I did have a tad bit of stutters. I then went to GE-Proton9-25 and found there were a lot less slow downs and was perfectly playable. I recommend however to enable vsync as I found without it the game had some issues. You may also have to change from low to ultra whatever is suitable for your machine. So it may or may not work for you. At least for me I have vsync enabled and its on Ultra and as said very little issues with stuttering and I wouldn't even say it bothers me. How I have this setup I feel is perfect and should run well for others. Not all machines may have the U3 Fatal Error issue but mine did so I had to resort to the launch code I'm using. If you have an issue when you load the game in a level and there's major stuttering, i recommend exiting the level and entering again. This may solve your issue, have fun!