Recently I implemented an alternative search based on fdroids app index. The UI is not polished or useful on mobile, but it meets my needs. Also, since it’s a hobby project, it can go offline or break at any time. However, maybe it’s useful for someone else.
It isn’t possible to filter directly for categories or anti-features on duckduckgo. Also getting a single list of fitting apps is convenient for me.
I had a similar impression. It seems to be difficult to get a change of the search into upstream. That’s why I decided to start a new project, as suggested here.