I was totally the same way when I wrote my first novel. I had the general flow of the story in my head with a few scenes, and somehow ended up with a 65k word manuscript just out of my head. It was a disjointed, poorly paced, poorly written, character arc-less, boring mess of a story.
It was a good learning experience though. I found out that I’m not a pantser. After learning some frameworks (Abbie Emmons on YouTube has some really helpful resources for Planners to use) and getting a full outline written, I’ve found writing my third novel to be so much easier.
I haven’t heard of Fabula cards, I’ll have to check it out. I’ve honestly just been using the sticky notes app on my Mac and the card-based overview in Scrivener.
To expand a bit on point 1 - you won’t truly know what you are until you try. I wanted desperately to be a pantser, wrote a terrible novel, and hated every moment of it. Then I tried planning and I’m having a much better time.