I heard that YouTube recently updated their API therefore YouTube video doesn't work on product page. Have you found the fix yet? I tried all three below on my product page (Debut theme) but the video doesn't show up to end user:
1) Direct video upload
2) Use YouTube URL
3) Add YouTube URL to HTML editor on product descriptions
I have not heard of this but I just added a YouTube embed to a product page without issue:
<iframe width="560" height="315" src="https://www.youtube.com/embed/XyNlqQId-nk" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
Does that snippet work for you? If not, can you provide a link to a page where it's not working?