@citizan Glad to know that it is working fine on the live page and the error is only in the Visual Builder.
However I have just tested the plugin on a completely fresh installation of WordPress and the latest version of Divi theme and I don’t get this error.
You can also confirm this by using https://tastewp.com/ to setup a temporary WordPress website easily and quickly, upload the Divi theme and then install the Post Carousel plugin. I see the Hello World post in the Visual Builder when I add the module and the Post Carousel works fine inside the Visual Builder.
So this is not a generic issue and it seems to only happen under certain conditions.
Would it be possible for you to export the posts you have on the website through WordPress Dashboard > Tools > Export and also export the Divi layout of the page where you add the Post Carousel module to [email protected] so I can try to recreate the issue on my end find out why it is happening.
https://www.elegantthemes.com/documentation/divi/library-import/