Disney+ web application disables video popup button for some reason. You can add a bookmark with the following content to enable it back.

javascript:document.querySelectorAll("video").forEach(video =>{video.removeAttribute("disablePictureInPicture");})

Open a video and click on the bookmark, and video popup button for that video is enabled.

This tip was taken from: https://github.com/polywock/removeDisablePiPAttribute