We’ll have to say goodbye to the familiar interface in March.
Google has announced the imminent abandonment of the classic interface of the desktop web version of the YouTube video service.
Forced switching of users to the new Youtube design will begin in March 2020. Now both options are available to users and you can switch between them. However, in March this will become impossible, only a new option will remain.

Users of the classic version will soon begin to receive alerts inviting you to switch to the new version of Youtube. You may need to update your browser to navigate.
Google began to change the design of Youtube in 2017, when the principles of design of Material Design were introduced, and then continued this useful business. The final version was presented in November 2019. The new design includes many modern features, including a now fashionable dark theme and a more convenient viewing queue.