Abs are just like any other muscle, you can’t spot burn fat. And 30 minute ab blasting workouts arnt the most effective way to get there (the only reason the are sometimes effective is it burns more calories than doing nothing, and stimulates muscles to some degree, but does neither as effectively as focuses cardio and focus abdominal strength training)
If you want abs or a toned stomach the only thing you can do is lose fat overall, and build muscle. When building ab muscle it’s just like building biceps or your booty. Resistance training, particularly progressive overload is the best way to make it happen.
Also time your cardio during a fasted state, and try and do the strength training right before or after eating to break your fast. And eat plenty of protein so your body can recover and build those muscles
Ab exercises will help develop the muscles but won’t do anything to help you see them. Visible abs are a matter of body fat percentage. Btw, the body fat percentage required for “visible” abs is really at or near the healthy minimum.
As for ab exercises, sit-ups and crunches can cause back issues for some people. Planks are healthier and also help develop your back muscles. Otherwise, just keep doing what you’re doing.
Check out AthleanX on youtube. Jeff Cavalier is pretty good, especially for avoiding injury. Do a search on his channel for abs and you’ll see a treasure trove of tutorials for movements that work. This will make your core strong all through upper and lower abs but visibility as others have stated is done through diet. Jeff Nippard is also very good, very polished content delivery and well researched.