The feature couldn't have been very popular, and TechCrunch spotted a support page update that says Duplex on the Web will be dead by the end of the month.
Google's automated mouse clicker theoretically would have scaled well because it could bring voice support to a website without needing any work from the website owner.
Google's support page says that "Duplex on the Web is deprecated and will no longer be supported as of later this month.
Any automation features enabled by Duplex on the Web will no longer be supported after this date." Google told TechCrunch, “By the end of this year, we’ll turn down Duplex on the Web and fully focus on making AI advancements to the Duplex voice technology that helps people most every day.”.
With no comprehensive list of accepted commands for Google Assistant, it's not clear how anyone is supposed to learn about these features.