How can I turn off the download button from my html video?

Chrome is putting that download button by default on every html video and audio element, and they don't give developers an option to not to display that, so we don't really have control over this.

There is a css trick, which seem to work, when the video is not too small:

video::-internal-media-controls-download-button {
    display:none;
}

video::-webkit-media-controls-enclosure {
    overflow:hidden;
}

video::-webkit-media-controls-panel {
    width: calc(100% + 30px); /* Adjust as needed */
}

so you could use this by adding it to your theme's style.css file (or your template's any css file, which is called in), but this doesn't give any protection against downloading your video, because people could just right click on it, and choose to save like that. And even if you would block the right clicking on your website, it is still very easy to download it for someone, who knows basic html. Probably this is why Chrome chose to just put a button there, and let it happen. So what we would suggest is to ignore it, because if a video is up in your website in any way, that can be downloaded. And we don't really support this, so if the css code doesn't work, then you will have to find other solutions yourself. Maybe upload the video to YouTube instead, to not to have a download button.