WordPress Multisite Network Shared Custom Post from Main Site using single-CPT.php

I seem to have solved it with the following code which I cobbled together from other answers after searching last 24hrs.

It gave an error until I removed the restore_current_blog at the end of the function.
As this should only be used by the singular page for the custom post type, I am hoping, it seems to work ok now. I am able to read and display single-CPT on the child site pulling in complete data.
So a CPT living on master: master.com/tax1/tax2/yax3/single-CPT
also works on slave: slave.com/tax1/tax2/yax3/single-CPT even though it is not there.

add_action('pre_get_posts', 'custom__pre_get_posts');
function custom__pre_get_posts($query){
    //Get access to global variables
    global $blog_id;
    global $wp_query;

    //Make sure we're not in admin, only run on the main query and don't run on our primary site
    if($query->is_admin || !$query->is_main_query() || $blog_id===1){

    //Try running the query
    //$test_obj = $query->get_queried_object();

    //If we didn't get a result then the page wasn't found
    if(in_array($query->get('post_type'), ['###MY-CUSTOM-POST###'])) {
      //Switch to the main site
      //Reset the query using the same args as the original (the previous reset changes $wpdb)
      //$wp_query = new WP_Query($query->query_vars);
      //Re-query the object again. We might need to perform more sanity checks here
      //$test_obj = $query->get_queried_object();
      //Switch back to our current site
      //This is a normal query for a page that exists, we don't need to do anything