Beware! The Posts Carousel element is a part of the Raven elements. Raven is an exclusive plugin developed by Artbees which represents new useful elements to Elementor. In order to see the default Elementor Posts, you need to look for it in the Elementor knowledgebase.
In order to add the Blog/Portfolio posts in carousel to your layout in Elementor:
1. Add a new page or edit an existing one.
2. Click on Edit with Elementor button.
3. From the left dashboard, search for a Posts Carousel.
4. Drag and drop the Posts Carousel element to your page.
5. A new dashboard on the left will open with the element’s settings.
6. From the Content tab and in the Content section, set the source to the post type from which you want to display the posts. (i.e Blog).
7. Edit the settings and Update the page.
Note: You can refer to this article, if you want to add the posts as a regular Posts element and without carousel.