This is really fun and there are a lot of things I like! The 3D looking spaceships are a nice change of pace from all the pixelated spaceships in other shmups. The sound effects are very realistic and satisfying. I also like how the game starts off simple with not too many spaceships but gradually gets more difficult. I could definitely see myself playing more of this.
One minor suggestion:
Have all of the control scheme text aligned to the left instead of centered. This will make it easier to read.
I know it's just a demo but great job! And I'm even more impressed to see that this was made in Godot.