The IP of restrict.youtube.com is to be mapped to www.youtube.com, m.youtube.com, etc. So in the host file
216.239.38.120 www.youtube.com
216.239.38.120 m.youtube.com
216.239.38.120 youtube.googleapis.com
216.239.38.120 youtubei.googleapis.com
216.239.38.120 www.youtube-nocookie.com
Personally, I'd use the host record as a backup/alternative if the CNAME method isn't working by itself.