Can you name the error? As it is working properly for me as it is.

The name of issue or what?

Why do you think you had to fix the full screen video. I see it properly.

Oh I see, there were some mistakes, but anyway, why would you change the position to fixed and remove the z-index.

This should be ok:

#myVideo {
    position: absolute;
    z-index: 4;
    right: 0;
    bottom: 0;
    top:0;
    right:0;
    width: 100%;
    height: 100%;
    background-image: url(imgs/flowers.jpg) no-repeat; 
    background-position: center center;
    background-size: contain;
    object-fit: cover; /*cover video background */
}

I have some problem with this z-index (dont show any text) so i change it.
There are two times "right" and I think that "left and top" is enought ;)

You can probably leave it like this:

        #myVideo {
            position: absolute;
            right: 0;
            bottom: 0;
            top:0;
            width: 100%;
            height: 100%;
            background-image: url(imgs/flowers.jpg) no-repeat; 
            background-position: center center;
            background-size: contain;
            object-fit: cover; /*cover video background */
        }

I have some problem with this z-index (dont show any text) so i change it.

z-index might not be necessary, but of course, as it is absolute positioned the text on that section will have to be placed after the video element or be given a higher z-index.
That was probably your problem. You were maybe placing the text before the video element or with a lower z-index.