A few days ago I purchased Portal Knights on Steam for my library. I'm on Ubuntu Linux for my desktop and I was unable to get the game to load. After some research, I found I needed a new file that should have been created on game startup. The file is "portal_knights.cfg". I read that if you create it on Windows you can simply copy it to your Linux partition. And since I have a dual-boot, I was able to do just that. For others, not so fortunate, I'll provide my file here for reference. Your Mileage May Vary (YMMV).

{
    "gamebuild": "",
    "graphics": {
        "api": "Direct3D11",
        "adapterPlatformId": "4318,11524,0,0",
        "displayName": "\\\\.\\DISPLAY1",
        "width": 1920,
        "height": 1080,
        "refreshRateNumerator": 144000,
        "refreshRateDenominator": 1000,
        "windowType": "WindowedFullscreen",
        "windowPosX": 0,
        "windowPosY": 0,
        "windowSizeX": 1920,
        "windowSizeY": 1080,
        "presentationInterval": 1
    }
}