Thank you for the guide, I would like to mention that on the second "Reboot recovery" my phone's stock recovery came up, and I used it for the second flash.
There is a problem with the "reboot recovery" step here, my phone did not have a recovery installed so it was booting to the bootloader, I had to use fastboot boot twrp.img to temporarily boot TWRP again to wipe userdata and to install Magisk.
Everything worked well after that... but unfortunately I encountered another issue which put me in a "boot loop"
I was changing the lock screen settings when it suddenly went back to the "OMNI" boot animation screen, and then once it reaches the lock screen, it repeats.
I don't think the device is actually restarting, but the boot animation is played in a loop... I think something in lock screen is wrong and it is crashing the entire phone
How do I fix this without wiping the data?