THIS IS SOLVED
I have just done a hard mod on my New 3ds XL on 11.4.0 following these two guides :
"https://3ds.guide/installing-boot9strap-(hardmod)"
"https://gbatemp.net/threads/tutorial-noob-friendly-nand-dumping-2ds-3ds-3ds-xl-n3ds-n3ds-xl.414498/"
I was able to dump the NAND and...