How to Hide WP Mail SMTP Plugin’s Top Level Admin Menus

Why this is necessary as once you have configured the plugin, you rarely ever need to look into it.

If anyone else is looking for this feature, this is how it’s done:

function move_wp_mail_smtp_to_submenu() {
// Remove top menu 
remove_menu_page( 'wp-mail-smtp' );

// Add submenu page to tools
add_management_page( 'WP Mail SMTP', 'WP Mail SMTP', 'manage_options', 'wp-mail-smtp', 'toplevel_page_wp-mail-smtp' );
}
add_action( 'admin_init', 'move_wp_mail_smtp_to_submenu' );

Remove Unnecessary CSS of WP Mail SMTP on all pages

wp_deregister_style('wp-mail-smtp-admin-bar');

https://wordpress.org/support/topic/option-to-hide-plugin-menu-from-top-level/

https://plugintests.com/plugins/wporg/wp-mail-smtp/tips