Could someone explain me what’s incorrect in what I did ?

You need to turn left on the pipe with shell at the end as you going up and You need to clip into the pipe try jumping from the middle or last block while holding right+down!

The first part of the set up was correct but the last shell was supposed to be on the right not the left. Listen to what Falcon said about the pipe clip. The last step during the glitch scroll. When Mario is scrolling down you need to hold down+right and press jump when he comes out the pipe on the bottom. If everything is done correctly you should trigger the ending cutscene

toutes t'es manœuvres était bonne sauf qu'a la fin pour rentrer dans le tuyau invisible tu sautais trop haut, tu doit sauter moins haut et appuyer sur la flèche bas pour rentrer dans un tuyau :)