If you sell only virtual/downloadable products with woocommerce there is no point of collecting Billing details , if you think the same then here is the snippet to hide the billing details and order notes from woocommerce checkout if Virtual product is in cart.
How to add this snippet?
You can add this snippet to your child themes functions.php , We don't recommend adding code to your main theme if its not developed by you. Otherwise you can use a simple plugin https://wordpress.org/plugins/code-snippets/
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