YouTube Download not available
I am from India where we have this feature and didn't know that it is not universally available
From YouTube help
You can download only in these countries


Algeria

Egypt

Ghana

India

Indonesia

Jordan

Kenya

Libya

Malaysia

Nigeria

Pakistan

Philippines

South Africa

Thailand

Vietnam

Yemen



Reasons not stated but on reddit there is an explanation given two years ago by a user who seems to be from YouTube
Alternate option is to use YouTube Red