Am not sure if Content Graph supports filtering on nested block properties within content areas. However you could do something like this (unless you find a query example with filter)

Get Page types you need by expanding the content area on the types you are looking to filter on and then do client side filtering for the word in the expanded item.

Hi Frida,

Here is a sample query about querying block on a content area in page

query MyQuery {
  HomePage {
    item {
      MainContentArea {
        ContentLink {
          Expanded {
            Name
            ... on FreeTextBlock {              
              HeadingBlock {
                Heading
                HeadingStyle
                HeadingAlignment
              }
              Content
            }
          }
        }
      }
    }
  }
}