Video in bright sunlight and the camera's automatic exposure control will select a faster shutter speed, there will be less motion blur.
This looks possibly stressful to your back. ? Compare to videos of high level servers.
There does not appear to be an angle between the forearm and racket at impact. The wrist looks to be at a very stressful angle. Stop experimenting until you understand the safety issues. You give the impression that you are trying to impact the ball as high as possible. ? That is not true for high level servers, look for the angles of their body and arm at impact, they are not vertical.
I look at high level serves based on internal shoulder rotation and point out differences.
I don't see the racket rising when it impacts the ball but the frame rate and motion blur make that difficult to see. ?
I don't see an angle between your forearm and racket leading to impact. Your hand probably tracks in the direction of the ball, but the hand of a high level player tracks to the side at considerable angle.
Your back and your wrist at impact look stressed, possible injury risk. ? Compare to wrists in high level serves.
Club player kick serve impact showing wrist and angle of forearm and racket at impact. With your wrist angle how can the racket strings rise at impact?
https://i.vimeocdn.com/video/472939059
Another video showing a high level kick serve.
https://vimeo.com/27528701