Can I add search engines to Safari (beyond the 5 that are selectable in settings)?

I want to use different search engines other than Duckduckgo, Google, Yahoo, Ecosia and Bing, but I can't see how this is possible in the Safari settings as there doesn't appear to be a way to add my own search engine. I would like to use a Searx instance as my default, for example. Or even Startpage, but it doesn't seem possible to change this in Safari's settings. I'm on macOS Big Sur.