How to hide the menu item created by the theme in WordPress admin panel?

1. As a temporary solution, add below script to the function.php file

wp_enqueue_style( 'flatsome-hide', get_stylesheet_directory_uri() . '/css/flatsome.css', array('flatsome'), '1.0' );

Crete a CSS file called “flatsome” inside your CSS directory, or whatever you prefer, make sure you update the name and the path on function.php.
Then inspect the menu class and hide it using display: none

2. The second method, use a filter in fuction.php

function custom_menu_page_removing() {
    remove_menu_page( $menu_slug );
}
add_action( 'admin_menu', 'your-MENU' );

https://codex.wordpress.org/Function_Reference/remove_menu_page