There is currently a problem with searching using the search box in the center of the screen on both https://start.duckduckgo.com and https://3g2upl4pq6kufc4m.onion when JavaScript is disabled.

Searching from the URL bar works correctly. I have reported this bug to DuckDuckGo in two places. If they are not able to fix it soon I may have to do something different with the default homepage.

In the meantime, users can work around the problem by using https://duckduckgo.com as the homepage if JavaScript is disabled, or using a domain setting to enable JavaScript for *.duckduckgo.com or 3g2upl4pq6kufc4m.onion.

Update: the problems with https://start.duckduckgo.com have been resolved by switching the default homepage to https://duckduckgo.com/?kao=-1&kak=-1. The problems with https://3g2upl4pq6kufc4m.onion remain and DuckDuckGo seems uninterested in fixing them. For the time being I have left it as the default Tor homepage because it confirms that Tor is working when it loads, but if any of the other search engines produces a .onion search page that works with JavaScript disabled I will switch to them instead.