You need to install a SEO plugin to setup featured image for social media websites. after setting up the plugin, Make sure that you clear the page cache in WordPress.
I see. Stuff like these is usually controlled by SEO plugins. Perhaps your previous theme had this feature? However, usually, as mentioned it’s controlled by SEO plugins.
Twitter will display the image if it can find the relevant meta tag in the head of your site.
And that meta would be added by RankMath.
I checked one of your posts and i see that the necessary meta tag has been added.
See here:
The Theme has no control over this, we don’t add meta or interfere with the meta, its 100% RankMath, if the image is not displaying then it would be best to check with RankMath.