Reproduce bug

Install dependencies

yarn install

Using build and start: OK

yarn build && yarn start

Visit /: OK. Visit /foo: OK.

Using dev server: 404

yarn dev

Visit /: OK. Visit /foo: 404 despite the rewrite from /foo to /.

Using rewrites declared in next.config.js

Edit next.config.js, use the in-file rewrite declaration.

Visit /foo: OK.