Not able to create sub menu WordPress plugin development

Hey there i am trying to create a coming soon plugin which will have 3 menus like

Coming Soon -> All Templates -> Options

First is created working perfectly but whenever i try to add submenu below that its not showing Note: i am trying to create a plugin similar to seedprod https://wordpress.org/plugins/coming-soon/

i dont know why that submenus are not showing below is my code is there anything i am doing wrong?

<?php
/*
    Plugin Name:my-coming-Soon
    Plugin URI:https://www.troeon.com/troeon
    Description:this is a good plugin
    Author:Troeon
    Author URI:https://www.troeon.com
    Text Domain:my-coming-soon
    Version:1.0.0
*/

define("PLUGIN_DIR_PATH", plugin_dir_path(__FILE__));
define("PLUGIN_URL", plugins_url());    
define("PLUGIN_VERSION", "1.0.0");


function cpt_coming_soon() {

    add_menu_page("Troeon coming soon", "Troeon coming soon", "manage_options", "troeon_coming_soon", false, "dashicons-heart");


}

    add_action("admin_menu", "cpt_coming_soon");
    add_action("init", "template");


function template()
{

$labels = array(
    'name'                  => __( 'Templates'),
    'singular_name'         => __( 'Template'),
    'menu_name'             => __( 'My Coming Soon'),
    'name_admin_bar'        => __( 'Template'),
    'add_new'               => __( 'Add New'),
    'add_new_item'          => __( 'Add New Template'),
    'new_item'              => __( 'New Template'),
    'edit_item'             => __( 'Edit Template'),
    'view_item'             => __( 'View Template'),
    'all_items'             => __( 'All Templates'),
    'search_items'          => __( 'Search Templates'),
    'parent_item_colon'     => __( 'Parent Templates:'),
    'not_found'             => __( 'No Templates found.'),
    'not_found_in_trash'    => __( 'No Templates found in Trash.'),
    
);     

    

$args = array(
    'labels'             => $labels,
    'description'        => 'Description',
    'public'             => true,
    'publicly_queryable' => true,
    'show_ui'            => true,
    'show_in_menu'       => "troeon_coming_soon",
    'query_var'          => true,
    'rewrite'            => array( 'slug' => 'Template' ),
    'capability_type'    => 'post',
    'has_archive'        => true,
    'hierarchical'       => false,
    'menu_position'      => 20,
    'supports'           => array( 'title', 'editor', 'author', 'thumbnail' )
   
);

register_post_type( 'My Coming Soon', $args ); }

function submenu_func()
{
    add_submenu_page("edit.php?post_type=My Coming Soon", "Troeon Options", "Troeon Options", "manage_options", "troeon-options", "submenu_callback_func");
}
add_action("admin_menu", "submenu_func");

function submenu_callback_func()
{
    echo "hii";
}

function coming_soon_assets()
{
    wp_enqueue_style(
        "cs_style",
        PLUGIN_URL."/my-coming-soon/assets/css/style.css",
        '' ,
        PLUGIN_VERSION 
    ); 

    wp_enqueue_script(
        "cs_script",
        PLUGIN_URL."/my-coming-soon/assets/js/script.js",
        '' ,
        PLUGIN_VERSION,
        false 
    );
}

add_action("init", "coming_soon_assets");