> 6. right click the DDG search dialog box and select “Add to Search Bar...”

I'm having exact same problem :/

However it looks like DDG removed opensearch funcionality as mentioned above and the only way to add it is to install extension?! :/
posted by <hidden> • 2 years and 1 month ago Link

Please reference my answer in your other post.
posted by x.15a2 Community Leader2 years and 1 month ago Link