a lot of people’s form is wrong on cable crunches. The abs perform back flexion, meaning all bend should be in your back. A lot of people are pivoting at the hip joint on cable crunches, which the abs don’t do at all, the adductors do. Make a conscious effort to be still at the hips and crunch at your abs. I like to sit on my heels and position my body directly under the cable so I don’t have much room to move my hips
another tip, the range of motion of the movement when you take your hips out of the movement isn’t very large, and it can be kinda awkward to get used to an exercise with a short ROM in my experience. Just be prepared for that and don’t be worried if you don’t feel like you’re doing a lot.