If you’ve created content as pages, and you’d like to convert them to posts, maybe to display them in the “blog” or “posts” module of your favourite page builder, you can easily switch between the available post types, using this simple plugin. While it hasn’t been updated for some time, tests on this site shows that it still works fine with Gutenberg, and Elegant Themes, creators of Divi, also recommends it. Just for testing purposes, this post is actually created as a page, and then converted to a post.
Extract from WordPress.org
This plugin adds a simple post-type drop-down to the post editor interface, allowing you to reassign any post to a new post type. It allows you to switch post’s type while editing your post. With bulk editing you can select all the posts in a certain type and convert them to a new type with one quick action. With block-editor (aka Gutenberg) support you can switch between post-types that use either the Block Editor and the Classic one, without losing any of your embedded content.https://wordpress.org/plugins/post-type-switcher/