Hi there,
first make sure you have the Blog module enabled in Appearance > GeneratePress.
Then in Customizer > Layout > Blog –> Featured images, there are 3 tabs: Archives, Posts, Pages. Select the Posts tab and Uncheck Display Featured Image
More info here:
https://docs.generatepress.com/article/adjusting-the-featured-images/
Thats a global change to remove them from all single posts. If need be there are options to selectively disable them on a post by post basis if you need ( let me know ).
And if you need to share any private details with us, as its your topic you can access the Private Information field in your replies, and only GP support can see its content.