Good game!
I think that this is an AMAZING first game, as you really well-choosed the graphisms, how they fit together and the idea is well executed. The transition are a bit too slow: I understand that you tried to write a nice story, but not all players play game for the stories, so having a “skip” option is always a good idea :D
The UI feels a bit wrong, especially for the gem sequence entering screen. Try changing the default font and feels of the UI for something that suits a bit more the overall athmosphere! But overall your winning sequence with the removing of the grayscale effect is SPOT ON! Congrats on that!
I’d say your best room for improvement are in animations: it’s usually (I don’t know godot that well) not hard to add a walking animation, even if it’s just a squash-and-strech one, and they add a LOT to the overall feels of the game.
The SFX sounded great :D
If you ever decide to make your own game fully (including graphism and sounds), a great tool to create your own 8bit sound effect is https://sfxr.me/ and a greater tool for pixel art / animation is https://www.piskelapp.com/
Good luck on your game-dev journey! Starting with godot is harder than unity I’d reacon, but I’m sure you’ll manage.