I'm glad you liked! For your source questions, this a Godot Engine game, so things are a little different:
1 - Is just a button with a simple command OS.window_fullscreen = true in GDscript
2 - The leaderboard is a free addon from SilentWolf that's pretty easy to implement
And thanks for the design comments, remebering the position of the religions was a "hidden" mechanic and I appreciate that you notice it!