Losing a belly at 40

Nobody loses weight proportionally and we all tend to have a spot or two that like to hold onto fat longer than other areas of our bodies. It sounds like yours is your stomach, which is pretty common in men. The best thing to do is stick with losing fat. Ab/core exercises will make your muscles stronger but until you lose the layer of fat, you'll still have the belly. You can't really spot reduce fat.

I lost mine when I was going through menopause, so you can do it at almost 40
Eat at a maintainance or reasonable calorie deficit while incorporating a progressive strength training regime.

This can be body weight, dumbbell, or barbell. The emphasis is you lift things that are heavy for you, or with the body weight, for example, once you can plank for 60 sec, start adding side planks.
Just keep increasing the difficulty level.

As your abs are engaged in all exercises a good well rounded routine will help retaine your LBM and strengthen your abs. Specific ab exercises aren't necessary.

Fat loss is needed, and unfortunately for a lot of us the abdomen holds on to it longest

Cheers, h.

In my experience, weight loss happens through diet modification. Exercise builds strength and endurance. Unfortunately, you can't target where the weight will come off. It comes off everywhere.