There’s a Kagi safari extension that will redirect any searches to Kagi. I still set my default to DDG because I think the extension intercepts after the request has been sent.
I'm pretty sure that every non-Google, non-Bing search engine on this list (Yahoo, DuckDuckGo and Ecosia) is actually powered by Bing. So really Apple is restricting me to two search engines: Google and Bing.
*IMO DDG is the only viable alternative to google in the apple search selection list