I'm glad you thought it looked interesting enough to want to check out Castor after seeing Manly's playthrough :3 For Linux, I'm gonna be zero help because I have no idea how the heck they work, unfortunately :( I don't even know anyone with Linux that I can ask to help me test those builds. I just use the default build settings on Unity and hope it works >.<
For Windows though, you're not the only person to experience that problem! Another user described the exact same thing happening to them.
Now, this is the first ever game I've made in Unity, and on the deadline night of the jam, I made my first ever build and encountered this very problem myself. After much panicking that I was gonna miss the submission deadline, I managed to figure out that it was the file type of the video on the title screen that caused the problem for me. I had a .ogv video playing. As soon as I changed it to.mp4, it was fixed on my PC and laptop. So, I'm wondering if it's the video file on the title screen still causing problems even though it's fixed for most people.
Last night, I uploaded a possible fix for the other person. If you go to the available files to download, look for the one called 'DD possible fix for LoneDeru'. It's a Windows build and what I did was I got rid of the video background on the title screen and replaced it with a static .png file instead to see if that fixes the problem. Give it a go and let me know if it makes any difference :3 If not, I'm gonna have to ask for some help from other people using Unity because I don't know what else could be causing it >.< I would have guessed possibly a resolution issue, but my laptop is an old windows laptop with a weird/uncommon resolution, and it works fine on that. *Fingers crossed* that removing the video helps anyhow!