After you complete the migration and replaced X-Cart 4 store with new X-Cart 5 one, you need to put the following code into X-Cart 5’s .htaccess file.

  RewriteCond %{QUERY_STRING} cat=([0-9]+)
  RewriteRule ^home\.php$ cart.php?target=category&category_id=%1 [L,R=301]

  RewriteCond %{QUERY_STRING} productid=([0-9]+)
  RewriteRule ^product\.php$ cart.php?target=product&product_id=%1 [L,R=301]

  RewriteCond %{QUERY_STRING} pageid=([0-9]+)
  RewriteRule ^pages\.php$ cart.php?target=page&id=%1 [L,R=301]
  
  RewriteRule ^home.php$ cart.php [NC,L]

This code makes sure that product, category and static pages which were properly indexed in your X-Cart 4, can now redirect to their successors in X-Cart 5 store.

If you use nginx web-server instead of Apache and .htaccess rules do not work for you, here is the equivalent of the same rules in nginx syntax:

#RewriteCond %{QUERY_STRING} productid=([0-9]+)
#RewriteRule ^product\.php$ cart.php?target=product&product_id=%1 [L,R=301]
location = /product.php {
    rewrite ^ /cart.php?target=product&product_id=$arg_productid;
}

#RewriteCond %{QUERY_STRING} pageid=([0-9]+)
#RewriteRule ^pages\.php$ cart.php?target=page&id=%1 [L,R=301]
location = /pages.php {
    rewrite ^ /cart.php?target=page&id=$arg_pageid;
}

#RewriteCond %{QUERY_STRING} cat=([0-9]+)
#RewriteRule ^home\.php$ cart.php?target=category&category_id=%1 [L,R=301]
location = /home.php {
    rewrite ^ /cart.php?target=category&category_id=$arg_cat;
}