According to YouTube, “Back in August 2017 we launched a new look for YouTube on desktop that introduced material design and new features like dark theme (check out the blog from 2017 here!). Note – up until now, people still had the option to opt-out of the new experience and continue using the older version of YouTube on desktop.”
However, the company notes that as a result of giving users the option, it meant that users were missing out on the new features and improvements of the newer design, and as such, the company has made the decision to phase out the old design in March.
YouTube adds, “If you’re using an older version, you will see a notification telling you to ‘Switch to the new YouTube’. You may also need to update your browser if it’s not compatible with the new version (We’ll let you know in the notification message if this is the case!)” So if you have been holding onto the older version of the interface, perhaps it’s time to start getting used to the new one.