My device Honor 8 Pro ( DUKE-L09 ) with EMUI B122 !
Here are the steps I've taken to install this ROM :
* unlocked bootloader
* reboot to bootloader and installed this
TWRP
* reboot device directly on TWRP by pressing comb keys ( while device was on bootloader mode , type "fastboot reboot" and at the same time remove USB cable and keep pressing Volume Up - device will reboot to TWRP )
* format data & reboot to TWRP
* re-format data & reboot to TWRP ( first time was a issue here because data can't be mounted )
* performed a factory reset
* while data was successfully formated and decrypted key was removed, I pushed via USB cable RROS 7.1.2 on Internal Storage ( sdcard )
* downloaded Gapps nano 7.1.2 x64 and pushed also to Internel Storage
* flashed RROS & Gapps at the same time ( with option add more zips )
* reboot to System
* and that was all - the device successfully booted to RROS 7.1.2 with Nano Gapps installed !