Originally Posted by Wharfe

Only a GuestSeat is not eligible for upgrade

https://www.etihadhub.com/content/da...t-aug-2021.pdf

You need an available F GuestSeat to be able to upgrade with miles at that 39,000 rate, there looks to be a lot of them available on AUH-LHR going by SeatSpy (Excluding peak times like Christmas). I think you can only do that sort of miles upgrade via the call center, and that'll take about 30 minutes on the phone while they tell you the system has issues.