per the spec at https://wicg.github.io/picture-in-picture/#disable-pip,
the attribute to control this is disablePictureInPicture
<video controls disablePictureInPicture controlsList="nodownload">
<source src="https://www.w3schools.com/html/mov_bbb.ogg" type="video/mp4">
<source src="https://www.w3schools.com/html/mov_bbb.mp4" type="video/ogg">
</video>
to achieve the same through javascript:
<video id="vid" controls muted>
<source src="https://www.w3schools.com/html/mov_bbb.mp4">
</video>
<script>
vid=document.getElementById("vid")
vid.disablePictureInPicture = true
</script>