is there anyway to resize the window, or it only able to open with fullscreen?
There's no in-game option, but you can use launch parameters to achieve this. If you're on Windows, create a shortcut to the executable, right-click it and go to Properties. In the General tab, you'll see the Target field, pointing to the executable. After the path, add a space and then
"-screen-fullscreen 0 -screen-width 1600 -screen-height 900", without the quotes. Replace the dimensions with your desired window resolution. You can make multiple such shortcuts for different resolution presets, e.g., if you want a separate setting for a 2nd monitor, etc.
Alternatively, if you have Steam, you can add the executable to your library as a non-Steam game and add the above parameters as launch options.
This will also work with different aspect ratios, btw, e.g., if you want to put the game on a vertical screen.
Use Alt+Enter to toggle between your custom resolution and full screen (be aware that the aspect ratio will be fixed, though, so you will encounter black bars, if the aspect ratios of your window and your screen are different. Also, toggling too often or too quickly can mess with the launch parameters and get you stuck in fullscreen again, so use that with caution!)
