Step 1: Visit a restricted YouTube video

Enter https://www.youtube.com/watch?v=is9sxRfU-ik into the address bar. If you are logged in to Google, Disable Restricted Mode. Alternatively, if you are not logged in to Google simply proceed to Step 2.

Step 2: Change the URL of the restricted YouTube video

Replace watch?v= in the URL of the restricted YouTube video with embed/. So https://www.youtube.com/watch?v=is9sxRfU-ik would be changed to https://www.youtube.com/embed/is9sxRfU-ik. The restricted video is now playable.