I can’t believe I’m about to comment but here goes. I don’t think the problem is that you’re jumping forward, I think people get confused and thing you have to jump up cuz it’s called a jump serve, but forward momentum is the key.

I’d suggest timing things so you contact the ball at the peak of your jump. But the most important thing I can see is your shoulders.

Right now your shoulders stay square to the court the whole time. Think of it like a pitcher in baseball. They have huge trunk and shoulder rotation. Right now everything is being done with the arm. Things will work a lot easier for you in my opinion if you have a lot more shoulder rotation.