Wireless Gateway Admin Tool (10.0.0.1) does not block sites properly

I have been trying deperately to block  https://www.youtube.com

 

No matter what I try it does not block it.   With remote schooling in play, teens do not need this distraction all day long.

 

I have followed the directions:  https://www.xfinity.com/support/articles/set-up-parental-controls-with-comcast-networking

 

This does not work.  Please help, this is extremely frustrating.