What's the link to the page? I found https://animedao.su/the-daily-life-of-the-immortal-king-season-2-episode-2-english-sub/ and the video plays fine in Opera.
Or, is it https://animedao.to/view/5065365900/? This one plays in Opera after I set PDFs to download at chrome://settings/content/pdfDocuments (which is weird to have to do that). I don't get anything about a sandbox. I have to click the play button in the center of the video area multiple times though to get the video to play. It's almost like the old click-to-activate behavior. But, the video still plays fine, even with Opera's adblocker and tracking protection on.