The seventh parameter passed to add_submenu_page()

I was able to track this down to the culprit function add_theme_page(). There

There was an additional parameter, per the codex for add_theme_page() that needed to be removed. Removing that seemed to help.

function fivehundred_register_admin_menu() {
  add_theme_page(
    '500 Settings',
    '500 Settings',
    'manage_options',
    'theme-settings',
    'fivehundred_admin_menu',
    plugins_url( '/ignitiondeck/images/ignitiondeck-menu.png' )
  );
}

add_action(
  'admin_menu',
  'fivehundred_register_admin_menu'
);

Fixed code

function fivehundred_register_admin_menu() {
  add_theme_page(
    '500 Settings',
    '500 Settings',
    'manage_options',
    'theme-settings',
    'fivehundred_admin_menu'
  );
}

add_action(
  'admin_menu',
  'fivehundred_register_admin_menu'
);

You could avoid the warning by adding the seventh parameter as null.

function fivehundred_register_admin_menu() {
  add_theme_page(
    '500 Settings',
    '500 Settings',
    'manage_options',
    'theme-settings',
    'fivehundred_admin_menu',
    plugins_url( '/ignitiondeck/images/ignitiondeck-menu.png' ),
    null
  );
}

add_action(
  'admin_menu',
  'fivehundred_register_admin_menu'
);

This Notice can be triggered by several variations/wrappers of the function add_submenu_page.

as of WP v5.8

• add_plugins_page
• add_users_page
• add_dashboard_page
• add_posts_page
• add_media_page
• add_links_page
• add_pages_page
• add_comments_page
• add_management_page
• add_options_page
• add_theme_page

To narrow the scope looking for the right function, we can modify the core file ./wp-admin/includes/plugin.php ( around line 1420 ) to be more verbose about it.

_doing_it_wrong(
  __FUNCTION__,
  sprintf(
    /* translators: %s: add_submenu_page() */
    __( 'The seventh parameter passed to %s should be an integer representing menu position. %s' ),
    '<code>add_submenu_page()</code>',
    print_r( $new_sub_menu, true )
  ),
  '5.3.0'
);

In my case the offending function was add_dashboard_page

add_dashboard_page(
  'Link Builder',
  'Link Builder',
  'manage_options',
  'mytheme-woocommerce-helper',
  array( $this, 'mytheme_woocommerce_helper_create_admin_page' ),
  'dashicons-admin-generic',
  2
);

Notice before edit core file:

PHP Notice:  add_submenu_page was called <strong>incorrectly</strong>. 
The seventh parameter passed to <code>add_submenu_page()</code> 
should be an integer representing menu position.  
Please see <a href="https://wordpress.org/support/article/debugging-in-wordpress/">Debugging in WordPress</a> for more information. 
(This message was added in version 5.3.0.) in wp-includes/functions.php on line 5535

Notice after edit core file:

PHP Notice:  add_submenu_page was called <strong>incorrectly</strong>. 
The seventh parameter passed to <code>add_submenu_page()</code> 
should be an integer representing menu position.  
Array
(
   [0] => Link Builder
   [1] => manage_options
   [2] => mytheme-woocommerce-helper
   [3] => Link Builder
)

warning/disclaimer/notes

Do this edit only in a development instance. WP core updates or upgrades will revert the changes. Plugins like wordfence will emit a warning and maybe revert the changes.

This same error is also being applied to argument issues in the add_pages_page() function.

For anyone else not using add_theme_page() or add_submenu_page() functions look for your usage of add_pages_page() and correct the arguments.

In my case I needed to remove the first argument which was null and give the page a title.