How to create a custom post-new.php page for plugin , no wp menu

I am currently creating an administrator plugin to manage and edit a large amount of separate information about establishments. I recreated a page with the list of articles which is linked to a new table in the database. Now I want to create a fully custom page of the same type as post-new.php - without the left menu and the top wordpress menu bar.

add_submenu_page( 'a-list', 'Add ', 'Add','manage_options', 'asso-add','atv_a_add');
function atv_a_add(){
      include plugin_dir_path( __FILE__ ) . 'adminpages/a-asso.php';
}

I have read in other post that post-new.php is not intended to be customized. How can I create a page that looks like post-new.php without the styling and access it from add_submenu_page ()?

For now the sub_menu_page redirects to wp-admin/admin.php?page=add. My page should link to wp-admin/custom-new.php or https://www.website.com/custom-new.php. But I wouldn't want to lose wordpress's default security.