Are ab exercises more useful to reduce belly fat than other exercises?
This is what I have as my summary and recommendations after all these years, which would be the combination of cardiovascular work and resistance training.
You can spend hours doing abdominal related exercises though if you would not be taking care of the nutrition and expenditure aspect, there would not be any belly fat loss that you would expect.
Be it Keto, Intermittent fasting, Atkins, OMAD and excluding the hormonal stuff that each diet has. The diets would generally require a higher expenditure as compared to intake for it to work.