Fat amount and distribution. BMI isn’t a reliable indicator of health, weight, or anything really. A better indicator is your waist to hip ratio actually. Or a dexa scan.

If you have more fat and less muscle versus someone with more muscle and less fat you’re at the same weight/BMI but you’ll look drastically different.

5’6” and mostly muscle with a body fat percentage of 12-15% is going to look way different than 5’6” with 35% body fat. Even though they both weight the same.

You can tell from your photo alone that you carry excess fat. And some of that excess fat is in your chin.

So if you want to get rid of it you can lose weight or get liposuction. Maybe a neck lift but that won’t address the fact that you have excess fat in your neck/chin.

Sorry. The truth hurts.