I refactored the notes activation system in order to trigger them when the player presses the spacebar and is near a note. Lots of work because I had to refactor the scripts.
A big search & learn was that green light blink when we press the spacebar.
I first wanted to "draw" a simple circle and make it grow around the note, but I struggled very much and found that only tons of sprites would make the job, so I gave up.
I found a pretty neat solution: particles!
I created a simple particle system that simply emits one static light that grows fast and disappear, and I found a way to trigger it manually via scripting when the player presses the spacebar.
And as a small cliffhangler for next step: I modified a bit the JSON for the tutorial scene, and it doesn't work very well, so I might have to look for this...