I do not know if it's in the right place but I put it to help others with the same problem.
Below are my exact steps, if that helps someone.
Download Magisk 19.3 TO INTERNAL memory OR SD CARD
1- In Fastboot:
fastboot flash recovery twrp.img
fastboot reboot and press vol+ to enter in recovery twrp
2- Disconnect the cable.
3- Install Magisk.
4-Reboot System. You're done! Launch MagiskManager. Device is rooted in the process, too. (Verify with a root checker app).
Power Off. Hit Power + volume Up - You should boot to TWRP.