For info, just installed it on OP3...
Made sure the device was on Oxygen OS 9.0.6.
unlocked the bootloader
Booted to fastboot - then booted TWRP 3.7.0_9
Formatted DATA
Wiped Cache, Dalvik/Cache, Storage and System
Rebooted to Bootloader (fastboot mode)
Used Installer 0.11.2 to test and started the install - device got picked up, no need to select
Left "wipe data" unticked
Followed instructions and UT installed as expected (Xenial).