DuckDuckGo redirect to html doesn't work
I believe I have narrowed down the problem to the new feature to disallow noscript (the HTML element) in NoScript (the extension). Setting DDG and Startpage to custom and allowing noscript made them work.
Because of how Tor Browser does NoScript options, restarting or changing security level will make the user have to enable the noscript tag again.
I recommend that the noscript tag be added on the safest.