I managed to flash TWRP on my mate 20 pro ( LYA-L09 ) but im positive it will work on all variants.
you must have bootloader unlocked. this will format your USERDATA so please be aware of this.
here is the following instructions to how i did it:
1. flash the twrp.img in fastboot - using command - fastboot flash recovery_ramdisk twrp.img once successful move to step two.
2. you need to format user data so that twrp to boot properly use the following command - fastboot erase userdata
once the erase userdata is complete, type in fastboot reboot and press enter.
3. you can now boot into twrp once in twrp you have to go to wipe and wipe data, please note this will take a very long time to wipe data so please be patient, it can take up to 1 hour or more, maybe less. so do it when you dont need to use your phone for a fair while. once the data has been wiped successfully through twrp, reboot back into twrp, wipe cache and then reboot back into twrp again. once booted back into twrp you are free to flash supersu or magisk
the link to twrp in my google drive is this -
https://drive.google.com/open?id=1PitrcNjMMynbWXP5jGfeNUqKdt5hJpfN