I was unlucky enough to run into a Unity error an hour before the deadline, crashing the build process every time I tried. Great jam, though. Many good submissions here!
Wow, I literally just figured this out, too, after hours of playing around trying to narrow down the problem. Yep, it's the terrain. If you're also using the URP-PSX shader, it's putting the shader on the terrain that causes the crash. Exporting seems to work now with normal textures, but I think building the terrain from scratch is probably the better option.