The Witcher 3: Wild Hunt - Complete Edition

I also had a lot of trouble trying to get this achievement on xbox series x. I tried just reloading, I tried to quit the game, I tried restarting the console. I went to CDPR support faqs and it says the console needs the cache to be cleared and I didnt try to unplugged it but this worked for me that I saw on another website:

Press the Xbox button in the middle of your controller and cycle all the way to the right in the new menu to your profile.
Click the “Settings” option.
Click the “Devices and Connections” option.
Click “Blu-Ray” in the new menu.
Click “Persistent Storage.”
Then click “Clear Persistent Storage.”

I had to kill golyath once more but it appeared the achievement right away! Hope it helps someone.

Here’s a way to do it in one shot. When Golyat is attacking you, he will swing his weapon in a downward motion, it’s one of his basic attacks, if you dodge while he’s being it down and press RB you will one shot kill him

I also had trouble getting it to unlock and the above comment taking about clearing the blu-ray persistent storage worked for me! I also didn't realize that it also gave me the "travel to Toussaint" achievement after I had done exactly what that comment said :)

UnknownScroll37, thanks a million mate, this worked perfectly, took me like 5 seconds, lol

Long story short: just spam RB from the start.