I tried this and I ended up with a broken h5ai, but it has shown the directories. I think that the index file is supposed to be a relative path (leading to "webrootdir/_h5ai/server/php"), while indexing the WebsiteRoot directory.
With your proposed config I got a very raw looking classic index showing the folders and "⚡ JavaScript disabled! ⚡⚡ Works best in modern browsers! ⚡powered by h5ai 0.26.1". Downloading the files did not work.