This is how I obtained this achievement so it 'should' work for anyone who follows the video below.
From reading some of the comments, it seems that this achievement is a bit buggy and may or may not unlock, even if you are doing it correctly.
After travelling to the "Luxury Apartments" fast travel point, make a new save file if you want the €$7,500 that you spend on the Cyberdeck back.
The Cyberdeck description tells you this but to activate Berserk mode, just hold
Note: The only reason the achievement doesn't unlock in this video is because I had already completed it, I was just replicating what I did to get it.
If you downvote the solution, please do let me know why so i can improve it.