Jim McLennan short video on the rotator cuff, impingement and serving
Todd Ellenbecker video on shoulder anatomy, impingement, and serving. At minute 8 he describes the same insure as McLennan but in more detail.
I looked at your videos but from the side view but I had a hard time especially seeing the shoulder orientation described above. Also, I don't know how to do YT stop action on my smartphone. With the camera placed behind the server and viewing along the ball's trajectory the shoulder orientation is easier to see.
Here is the view with the camera behind showing the shoulder orientation -
My shoulders are OK here but my wrist has an angle that was not correct, stressful.