First of all, based godot user!
I really like the transition between 3d and 2d, and the art is nice. Doesn't really fit the "otherworldly" theme at all, but that's fine. I only really have two pieces of feedback:
1: the gameplay doesn't feel very diverse. If you ever continue the game, I would recommend bigger more random islands and different types of skeleton enemies.
2: The red X that you have to dig up with your shovel feels really hard to hit with the shovel, and typically takes a while in my experience. Also, the only way to hit is is by being directly above it, so when you finish and the treasure chest comes up, it covers your vision.
I already said this on discord, but Ill say it again, if this really is your "worst" game you've ever made, you must be a pretty good game dev.