WordPress Featured Image meta box not showing

You might be facing this problem because your theme does not support featured images.

But you can easily add that support, so no worries 🙂

To quote the WordPress Theme Handbook:

Themes must declare support for the Featured Image function before the
Featured Image interface will appear on the Edit screen. Support is
declared by putting the following in your theme’s functions.php file:

add_theme_support( 'post-thumbnails' );

So just add that line to functions.php (of your own theme or child theme), and you will be able to see the Featured Image option after you save and refresh the admin area page.