1) the setting in past was available site-wide, is this no longer the case ? Must it be set page by page?
If you want to use it for multi pages or locations, use the layout element instead.
2) after attempting per the article, the contained setting specific to my home page, Iām not seeing the content contained.
I can see the setting has been applied to your homepage, but you are using a page builder, its content ignores the theme settings.
In this screenshot, you can see that the highlighted red area is the GP defined contained container, but page builder content just ignors it:
https://www.screencast.com/t/ojCdgrQzkhB