Thanks so much, really glad you liked it! 😊
For the menu, it's actually a shader material on a ColorRect. Took me a few hours to get it working — it simulates layers of stars rotating and approaching the player. It looked nice, but was pretty heavy on performance at first, but at the end it was ok with a bit of faking stuff and optimizing 😅. The same shader is also used during scene transitions, just with some extra acceleration and brightness added. Funny thing is, I originally made that as a transition effect first and only later decided to reuse it for the menu background. Turned out better than I expected!
In the actual game levels, I wasn’t too happy with the performance, so I simplified things. The shader just dims or brightens random stars, and the rest is a static starfield Sprite2D slowly moving on a predefined loop. Which actually fits the theme perfectly 😄