If not already present, add the follow lines to the config.toml file.
[outputs]home=["HTML","RSS","JSON"]
Docdock theme uses the last improvement available in hugo version 20+ to generate a json index file ready to be consumed by lunr.js javascript search engine.
hugo generate lunrjs index.json at the root of `public` folder if the site only has one language or within each language subfolder. When you build the site with `hugo server`, hugo generates it internally and of course it don't show up in the filesystem