_headers 404 (not netlify.toml)

Context:

  • The website is a static HTML+JS+CSS+images site deployed on Netlify
  • There is a _headers file to add basic authentication for certain directories (that works fine)

I would need to handle the 404 case, however everything I find is documented for netlify.toml. I am a designer and a front end developer, I cannot easily translate that kind of configuration from a format to another, and every article takes for granted that everyone can do that. Very frustrating.

Is there a way to add a line in the _headers file to say something like “whatever is not a valid URL, go to this other URL instead”? I’d very much like to avoid listing every valid URL in that process.

Thanks in advance for any explicit guidance that does not use the words “easy” or “simply” (those are notoriously frustrating in any tutorials/explanations).

It’s documented in both formats: Redirect options | Netlify Docs