From now until September 1, YouTube Premium subscribers can zoom in while watching videos. Some YouTube content shot for PC monitors or TVs might contain text or small elements that could be hard to discern on a smartphone screen. So it may help users see finer details.
https://www.techspot.com/news/95561-youtube-testing-pinch-zoom-feature-until-september-1.html?utm_source=dlvr.it&utm_medium=blogger
https://www.techspot.com/news/95561-youtube-testing-pinch-zoom-feature-until-september-1.html?utm_source=dlvr.it&utm_medium=blogger