I'd choose my brain, my feet and my gun over a knife for self defense. But, if I were to carry a knife for defensive purpose, a fixed blade makes a lot more sense to me. Imagine having to unfold your gun after drawing it, while you're full of adrenaline
Check out the Ronin 2 if the Yojimbo catches your eye. They also made a fixed pikal called the Reverse that was discontinued in 2018, you could probably still find one.
If I had to go with a folder, I'd pick a waved model like the Pikal or Endura wave.