The main shader which actually has the infinite tiling is shader_checker3_2.gdshader
Although it's called "checker", it doesn't strictly need to be a checker pattern, as you can actually use any texture image for the infinitely repeating pattern 😊
Unfortunately, I couldn't see an easy way to use this as the background as well, so we may need to fix that later.
The main shader which actually has the infinite tiling is shader_checker3_2.gdshader
Although it's called "checker", it doesn't strictly need to be a checker pattern, as you can actually use any texture image for the infinitely repeating pattern 😊
Unfortunately, I couldn't see an easy way to use this as the background as well, so we may need to fix that later.