I liked the music and artstyle! The mechanics are clear, is very relaxing. I think you are having problems with euler angles because I get the camera upside down somethimes and I aren't able to correct it in game, I have to reebot the aplication. I see you used Godot, check out the documentation to perform better rotations, or try making horizontal and vertical nodes to control each movement separately.
In my games I use something like:
- Cam_horizontal (Spatial with Script)
- Cam_vertical (Spatial)
- Cam (Camera)
- Cam_vertical (Spatial)
I control the rotation in each node separately and clamp only the vertical one (Everything in one script). The camera itself never rotates because the parents do the job.
Overall, is a very relaxing game, Good Job!