FIXED:
"Ok, so there's actually a really weird bug that's causing this I think. For some reason when it extracts using a gui archive manager, it's messing up all the java files.
What you need to do is go back into desktop, make a new SliceAndDice folder, and put the dice-win.zip inside that. You can delete all the files from the previous file extraction as well.
Once you've done that, right click in the folder and hit open konsole. Type unzip dice-win.zip and hit enter. It should extract all the files, but when you look in the folder instead of having hundreds of files you should just have a folder called jre, config.json, dice.jar, and SliceAndDice.exe. Add SliceAndDice.exe back to steam and set a proton version. It should work now."