functions.php

add_filter( 'job_manager_field_editor_js_conf_meta_keys', 'smyles_allow_featured_image_admin_only' );

/**
 * Allow featured_image to be set as admin only
 */
function smyles_allow_featured_image_admin_only( $config ){
    
    // Make sure admin_only_0 is in disabled fields first (_0 added for any checkboxes)
    if( isset( $config['featured_image'], $config['featured_image']['disable_fields'] ) ){
		// Flip values to array keys so we can unset admin_only_0 and still retain other values
	  	$flipped = array_flip( $config['featured_image']['disable_fields'] );
	    // Remove admin_only_0 from array
	  	unset( $flipped['admin_only_0'] );
	    // Flip back to values
	  	$unflipped = array_flip( $flipped );
	    // Set modified values
	  	$config['featured_image']['disable_fields'] = $unflipped;
    } 
    
    return $config;
    
}