https://duckduckgo.com/html/ and https://duckduckgo.com/lite are not
software. They are pure HTML. And accessing the results of a search query
is not Service as a Software Substitute (SaaSS):
Services such as search engines collect data from around the web and let you
examine it. Looking through their collection of data isn't your own computing
in the usual sense—you didn't provide that collection—so using such a
service to search the web is not SaaSS. However, using someone else's server
to implement a search facility for your own site is SaaSS.
https://www.gnu.org/philosophy/who-does-that-server-really-serve
The server-side code being free or not has no consequence on the visitor's
freedom (it has consequences on the service owner's freedoms, her business).
And the user cannot know the code that really runs on the server-side. She
has to trust the service provider. Or crawl the Web herself. Or
collaboratively (Seeks/YaCy). But what a waste of energy! As in "more power
plants" if most users start to crawl the Web themselves.