Funny thing about Keto. Most people who think they are doing it, aren't. It's a pretty extreme diet originally developed to treat juveniles with epilepsy. The average adult can't really sustain it for long.
I did it go into true ketoacidosis two years ago for a month by eating only eggs, 361 for 28 days or 12.9/day (0 carbs, 0 sugars, 70/30 protein/fat split). By the end I lacked any quick energy and had to calculate how I would expend what I had. I wasn't starving but I was mild - moderately lethargic.
Also, as noted, you can't exactly target belly fat. A pronounced belly may just be a personal genetic disposition (similarly, some women carry fat disproportionately on the hips) or you could have some very slack abdomen muscles. That would allow the gut to hang forward. In that case some targeted abdomonal exercises would firm the belly but it won't really target the fat that is there specifically.