If you're deploying your Preact app with preact-router to Netlify, you may find that trying to access anything other than the root of your website (e.g. foo.netlify.com/bar) will give you a "Page not found" error.

The recommended approach is to create a build/_redirects file and add this line:

/*/index.html 200

However if this doesn't work for you (it didn't for me), then create a redirects.txt file in your root folder, and add the following to your build command in Netlify:

npm run build && cp redirects.txt build/_redirects

References

Redirect Rules for All; How to configure redirects for your static site
Redirects not working