Thank you for your answer, @roboe! I had no clue where this animation resides, now I understand it better. If this is so untrivial it’s better to keep it like that…
Anyway, each time I’m asking myself that kind of question, I found answers on this forum, and each manipulation/customisation/change of OS/… bring me a better knowledge and view of how is this smartphone working 
Many thanks to this awesome community !
Concerning SN, I’m aware of the position of LineageOS and I respect them. What is interesting to me is that by doing the same steps as in OpenOS you can run the same apps on LineageOS 
In other words, by having the same functionalities as before I can therefore stay with LineageOS as main OS 