Edit:
If there is a black border on the edge of the video player

I can think of only 2 problems.
1. If the crop function has a problem There may be black borders on both the right and left. It doesn't happen on just one side.
2. In my code, I have added css for the video player to have a black background. which is normally not seen. If you see a black border on the right side, it means that your video player is larger than the content. Which I don't know why.

You can embed additional css into the youtube website, for example using the stylus addon to solve this problem (But you have to disable it when watching vertical video).

Try entering this code
.html5-video-container > video {
width: 100% !important;
}

How to use it, check out this video.
https://www.youtube.com/watch?v=dXTU15EAcCI

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What do you mean? Every video starts with settings for zoom at the beginning? Or what is desired is to have the default setting to automatically use zoom as previously stored.

But what I will say is that not every video needs to have the same zoom settings, and not every video needs zoom.