Google has confirmed that Discovery campaigns are indeed ending and will be replaced by Demand Gen campaigns from March 2024 >, whose beta you can request now. Starting in October, this type of campaign will be available to everyone, and from January to March, Discovery campaigns that have not been upgraded until then will be automatically upgraded. Discovery campaigns will disappear from April 2024.
Oscar Abad’s screenshot says that Demand Gen ads will appear on YouTube, Gmail, Discovery, and many other locations.
Anya Hwang shared a screen of how to ideally set up Demand Gen according to Google :
