Currently, comments can be found below a video on the YouTube for Desktop watch page
On mobile and tablet apps, comments show in a teaser that opens in an engagement panel when tapped by users. YouTube is now redefining the comment experience by enabling a comment teaser across all surfaces. The teaser will appear below the video. When clicked, it opens the comments on an engagement panel to look below the video. Comments will still appear below the video if a user does not engage in the comment teaser.
Implications to Marketers:
As YouTube enables a comments panel and teaser on desktop, its goal is to enable the user to continue watching the video while scrolling in the comments section. As such, marketers can find a way to highlight their product features more in the comment section of a video ad.