Honestly your form is pretty good. One thing I noticed that may help you is to stop jumping twice. You do a small jump forward then plant your feet and jump again to dunk. That first jump messes with your momentum and stops you from being able to jump as high as you can on the dunk attempt. Other than that everything else looks good. Let me know if that helps.
@Lautaro Banvenuto Yes you jump into your penultimate step. If you look at most dunkers on the internet they run into the penultimate whereas you jump into it.
I just watched jump technique #Jump Technique #1 (Basic) in the classroom section and added 2 inches to my vertical within 30 minutes!!! Thanks for the free training!