You can manually display zoomable featured image on single post screens via [zoom] shortcode.
Featured Image Zoom is a WordPress plugin that provides you a shortcode ([zoom]) for displaying zoomable featured images in single post pages on your WordPress website.
Start by installing ‘Featured Image Zoom’ plugin in WordPress
Upon activation, manually insert the [zoom] shortcode on post where you like to show specified featured image. The shortcode can be used anywhere inside your post content.
Simply insert the shortcode and PUBLISH/UPDATE your post content.
Once updated, your post will automatically grab associated featured post thumbnail and displays it in its original size with mouse over zoom functionality.