Restricted Mode was created to provide viewers who wanted to better control the content they see on YouTube with an option to choose an intentionally limited YouTube experience.
Viewers can choose to turn Restricted Mode on for their personal accounts. It may also be turned on for computers in libraries, schools, and other public institutions by the institution's system administrator. Viewers who turn on Restricted Mode cannot see comments on videos.
There are two ways a video can end up being unavailable when Restricted Mode is turned on.
Primarily, YouTube's automated system looks at signals like the video’s metadata, title, and the language used in the video.
Additionally, some videos may not be available in Restricted Mode as a result of human reviewers applying an age-restriction to a video.
YouTube's automated system isn’t perfect and it sometimes makes mistakes when assessing which videos to make available in Restricted Mode.