I’m not sharing any groundbreaking info in repeating this, but it’s important:
If you want washboard abs, or at the least for your ab muscles to appear on your stomach… you have to lose enough body fat for them to appear.
Making the ab muscles bigger won’t work in itself. They are covered in fat, and you have to burn that fat in order for them to appear.
You also cannot spot-reduce fat. Fat burns in a mostly even fashion from the inside out, all across your body. To lose the fat over your abs, you have to lose a corresponding amount of fat all over your body.
Plus, fat is first burned from the center of your body, from around your organs and muscles. As that’s exhausted, then your body moves to the fat closer to your skin. If you want to burn the surface fat over your abs, you’ve got to burn off all that other internal fat first.
This takes quite a bit of fat burning, and you typically need to diet down to a rather low body fat percentage before you can see ab definition. For men, this is about 10-12% max, and for women (who biologically carry more fat) this is around 16-19% max.
Yes, strength training helps you get there, not just because muscle burns calories (and in turn fat), but because more prominent muscle will begin to show through the skin and reduced fat layers sooner than less-prominent muscle.
However, strength training is only one part of achieving the needed definition for visible abs. Diet and body composition is the larger component. You can’t out-train your diet and composition.
So if you want six pack abs, maybe take it easy on the core training and ab workouts. While good for core strength, that’s only one minor component of getting your abs to show. You need to lose the fat in a healthy fashion for the muscle to emerge.