That’s a Netlify thing. Hugo creates a list of actual links, not a wild-card API point.
You probably just want to set the redirect rule in Netlify (check their docs/support). Creating a _redirects file is for setting redirects in front matter of individual pieces of content (and collecting it in a list).
I created this post, but then realized it is really a Netlify problem and not a Hugo problem. In case you are interested this change solved the issue on Netlify.
@gregraven in the Netlify community pointed out that I needed to use the force redirect with the 301! instead of the 301 directive. Otherwise, Netlify serves the page that is there.
See the definition of “force” in the “syntax” section of the Redirects docs page.