Hi Gabriel
From the video, it looks like you have the basic elements of the serve pretty consistent which is great. If you are not used to performing the serve it will take time to feel a little more natural. So keep up the practice and it will become more fluid with time.
One thing I can suggest here is when you throw the ball up to serve try to keep your bat low. At the moment your bat rises up with the ball which will make it difficult to perform the topspin variation because your bat needs to move slightly up on the ball. You can get both backspin or topspin from having a low bat. Check out this video on how to get more backspin by coming up to the ball. https://tabletennisdailyacademy.com/videos/backspin-serve/.
And check this video out for getting more topspin https://tabletennisdailyacademy.com/videos/topspin-serve/
General aims for your serve practice should be to increase the amount of spin you produce whilst keeping the serve low. Also, mae the practice fun. Give yourself targets and challenges to try and complete.
Keep it up
Answer for learning-the-side spin pendulum-serve
