WordPress add_menu_page未显示在后端

I am trying to create a custom plugin using the code below but the tab/link to the page is not appearing in the WordPress Dashboard and I'm not sure what I'm doing wrong. My company-admin.php file is located in my plugins folder inside a folder called company-admin. The file permissions for the php file are 644 incase that is relevant. Can you help?

add_action( 'admin_menu', 'my_admin_menu' );

function my_admin_menu() {
    add_menu_page( 
        'Company Admin', 
        'Company Admin', 
        'manage_options', 
        'company-admin/company-admin.php', 
        '',
        '',
        6
    );
}

I'm unsure if this is the correct way to navigate to my plugin but I used this link, correct me if its the wrong link;

https://mywebpage.uk/wp-admin/admin.php?page=company-admin%2Fcompany-admin.php

And what I get is the following error;

Sorry, you are not allowed to access this page.

Query Monitor
The message above was triggered by Core.

Call stack:

wp_die()
wp-admin/includes/menu.php:348

the permission file in wordpress must be 755 for work correctly.

For develop a plugin follow the wordpress official guide https://developer.wordpress.org/plugins/intro/

Let me know.

Try to add more code to your path. Instead of 'company-admin/company-admin.php', paste 'your_plagin_folder/company-admin/company-admin.php',

Edited
But more cleanest is using that way:

function wpdocs_register_my_custom_menu_page(){
    add_menu_page( 
        'Custom Menu Title',
        'custom menu',
        'manage_options',
        'custompage',
        'my_custom_menu_page',
        '',
        6
    ); 
}
add_action( 'admin_menu', 'wpdocs_register_my_custom_menu_page' );

/**
 * Display a custom menu page
 */
function my_custom_menu_page(){
    //print all what you need or include any pages
    include_once plugins_url('company-admin/company-admin.php', __FILE__);
}