I struggled to make a script from a loaded collection proxy send a message to the bootstrap proxies manager game object then I realised I checked action_id == 'start' instead of action_id = hash('start'). 
Those hash systems are beyond my comprehension. I don’t understand their purpose.
I also struggled to animate the alpha value of a sprite (I did it in a former project but I wasn’t able to find the information again).
I finally found the information in this thread. I don’t understand why that tint property isn’t listed in the sprite API.
Anyway, my title screen is almost finished. I update the itch page. If you have ideas about improving its layout or design, feel free to tell me. I’ll consider if I have the skills/time to change it.
Now, I have to take care of those asteroids…