https://www.theverge.com/2019/1/15/18184062/youtube-recommendation-feature-blue-bubbles-creators-search-trending

YouTube is testing a new recommendation format for both mobile and desktop users that use blue bubbles to suggest keywords, creators, and related topics to help browse through videos.

Screenshots obtained by The Verge show these blue bubbles in action. They appear just underneath the video player, and the idea is to help users filter recommendations. These are more specific recommendations than the videos that appear off to the side. The feature is currently being tested with a small set of people on both YouTube’s main desktop page and mobile apps.