Checked just for fun a few free WordPress hosting services and found the common bug: the featured image option is not available in the create post interface.
So far, the best solution was offered at hostinger.com:
“Edit the functions.php File of Your Theme
If you still can’t see the featured image meta box in the content editor or show post thumbnails correctly, your current theme most likely doesn’t support featured images.
In some cases, the code to enable the featured image functionality might be missing. You can solve this by adding the following code to the bottom of your theme’s functions.php file via an FTP client or a File Manager:
add_theme_support('post-thumbnails', array( 'post', 'page', 'custom-post-type-name', ));
Reload your admin dashboard and clear the website cache to see whether the featured image section appears when editing a post or page”.
Additionally, you may need to perform the following steps:
- Open your Post
- Click the post settings ICON to collapse the Post Options panel
- Refresh your page
- Once page refreshes, click the settings ICON to open the post options panel. Give it a second and the Featured Image option should become visible again.