See https://wordpress.stackexchange.com/q/343355 for details.

my-functions.php

<?php
add_filter( 'ajax_query_attachments_args', 'filterMediaLibrary' );

function filterMediaLibrary( $query = array() ) {

	if ( empty( $_POST['post_id'] ) ||
		( ! $post = get_post( absint( $_POST['post_id'] ) ) ) ) {
		return $query;
	}

	$parent_ids = get_post_ancestors( $post );              // add all ancestors
	$parent_ids[] = $post->ID;                              // add the post itself
	$parent_ids = array_merge( $parent_ids, get_children( [ // add all children
		'post_parent' => $post->ID,
		'fields'      => 'ids',
		'post_type'   => $post->post_type, // or set it to "any".
	] ) );

	$query['post_parent__in'] = $parent_ids;

	return $query;

}

What is the ids variable?
'fields' => 'ids',

See WP_Query::parse_query(). But it means to return the post IDs instead of all fields.