Honor 9 STF-L09 root is now available for users who are running Oreo B360. This method doesn’t require TWRP recovery to be installed on your phone, all you nee is just unlocked bootloader.

Honor 9 STF-L09 root Oreo B360

Instructions:

• This method is strictly for Oreo B360 (on other versions try at your own risk)
• Backup all important data on your phone
• Enable oem unlock in developer options
• Unlock bootloader of your phone ( How to unlock? )
• Enable usb debugging in developer options
• Download Latest Magisk Manager from THIS LINK and install it.
• Then download root files from THIS LINK
• Connect phone with PC
• Extract root files and then double click to open Install.bat file
• Follow on screen instructions, and your phone should reboot automatically with root installed.
• If all files flashed successfully then after reboot open magisk manager and tap on install it will download latest magisk and use direct install method
• Done

Source: XDA