OpenGraph global fallback not working

Hello,

Thank you for contacting Rank Math, and sorry for any inconvenience caused.

The default OpenGraph image is used only when:

1. You have not uploaded any featured image to the post.

2. You are not using even a single image inside the post.

3. You have not added any image to the social tab.

If you wish to force the use of default social image, please paste this code in your theme’s functions.php file:

add_filter('rank_math/opengraph/pre_set_content_image', function() {
	return true;
});

Here is a guide you can follow to add the filter:
https://rankmath.com/kb/wordpress-hooks-actions-filters/

Hope that helps.

Thank you.