Hi @ShannaKae,
As of the current version the Post Content block is not supported with frontend rendering switched on, but works perfectly on both the frontend and backend with frontend rendering switched off.
Note: For anyone reading this who is not clear on this yet, the frontend rendering setting/feature is not required to display the query on the frontend. Its purpose is to enable asynchronous loading of data of the frontend without refreshing the page.
If you specifically need frontend rendering switched on for your query (e.g. if you are using filters), then there are still ways of displaying the post content.
See this post for a similar ongoing discussion: