I see this referenced all the time. I haven't finished it myself, but from what I've read it's great.
$10 if you get the kindle version. https://www.amazon.com/Think-Like-Manager-CISSP-Exam-ebook/dp/B08D9L1BTF/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=1619647039&sr=8-2
Try Luke Ahmed. How to think like a manager. https://www.amazon.co.uk/Think-Like-Manager-CISSP-Exam-ebook/dp/B08D9L1BTF
I'm sorry to read that your preparation was not enough, or perhaps you entered the exam with the wrong mindset? The positive side is that at least you know what to expect next time, so you will enter the room with less emotions. Have you thought how to approach this exam differently next time? Perhaps this book might be useful for you: https://www.amazon.com/Think-Like-Manager-CISSP-Exam-ebook/dp/B08D9L1BTF
I came across some positive comments around it but myself didn't have enough time to go through.
Good luck, don't lose hope. You are one step away from it, just requires a bit of different thinking and luck. Yes luck. As many say there comes a point where you just gamble, myself I gambled at least 20% of the time. I was not sure at all. I picked two answers which made more sense to me and gambled.