Yeah, I use a self hosted searxng instance and Vanadium uses it as the default search.

However it's not obvious from the interface because it does this by using OpenSearch metadata gathered from an already completed search.

1) Open Vanadoum and go to your search engine of choice.

2) Conduct a search on the site and view the results page.

3) Got to Vanadium's settings > Search engine

4) The recently used search engine should be listed there at the bottom.