Thanks ultramag69 for info. Have you a guide for safe root? The only guide that seemed trustworthy that I found on the internet, unfortunately it was written in Chinese.
OK, if you are game...
As I said, my phone has bootloader unlocked so this worked fine, I don't know if it will work.
Essentailly you replace the stock recovery with TWRP TEMPORARILY, just one boot.
Download magisk systemless root file and put on sd card. Also activate developer settings and tick " USB Debugging".
Put TWRP file in folder with fastboot files on PC, hold shift and right click. Select "open CMD window here".
Put phone in fastboot mode. Attach to PC with usb.
Type in cmd window "fastboot devices", you should see you're serial number come up on another line if you are connected.
Type "fastboot boot twrp.img" - make sure the twrp file is named this.
You should reboot to TWRP. Make sure you DON'T select "Alter system files" as you're bootloader is locked.
Install magisk systemless root file from TWRP.
Reboot and see if it works...
As I said, I did this after I unlocked the bootloader but as magisk is a systemless root I don't see this not working.
That said there is always a risk when doing this sort of thing and I would urge you to unlock bootloader 1st as this makes it a bit easier to fix if things if something does go bad...