When you embed a video with HTML and then move your cursor before the video and hit Enter, the html/video is copied/recreated again.
Please see this video I recorded on your website:
https://www.loom.com/share/48633f60128940e5bb7767f134201cec
Example embed HTML from YouTube:
<iframe width="560" height="315" src="https://www.youtube.com/embed/SJBCHi1DMKo?si=eTiyLdMVzckZbhGm" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>