YouTube calls a vertical video a “Short Video”
Look for them on your smartphone. Go to your YT Home Screen and scroll down. YT has sold millions of dollars of advertising on these vertical videos and has paid out millions to the YT Creators.
Next year YT has plans to go worldwide with their plans for vertical videos as, “Short Videos”
YT has been testing vertical videos, below is how it looks on my iPhone.
Hope this helps. Gary