Excessive blood sugar causes insulin resistance; your body deals with the unused blood sugar by producing insulin, which causes your body to convert ALL that blood sugar to fat -- until you have none. Then your blood sugar is in a crashed state, you have various symptoms (weakness, shaking, thirst, etc.), and you're starving hungry. You then eat way more than you otherwise would have.
In the end, you eat too many calories and end up gaining weight. Not a smart plan.
Most foods created by God don't contain lots of simple sugars. There are a some starchy foods, yes, and some complex carbs are OK. But you need plenty of fiber with every gram of sugar you ingest. Apples, good. Apple juice, bad.
Don't listen to the advice of a young Gen Z twentysomething. When I was 20 I could also eat anything I wanted and not get fat. But that all changes when you get older. You can mock, you can brag about how you can "eat anything and not get fat" -- but trust me, your time will come. It's foolish to make fun of a group that you will NECESSARILY join at some point in the future, assuming you don't die a tragic death first.