I did what krypt0se suggested me to do and it worked, thank you anyway !Check out the steps here: https://topjohnwu.github.io/Magisk/ota.html
What I was suggesting was flashing the stock init_boot.img, running the ota update then patching the newest init_boot.img and flashing it back.
The guide above basically does this in an elegant and easy way through magisk.