How to append $metadata[‘sizes’] to metadata when using ‘wp_generate_attachment_metadata?

Although the suggested answer from admcfajn wasn’t the solution to the problem/question, it did lead me to look explore it further. Thanks admcfajn.

Assuming you are using either the default intermediate e.g. thumbnail or custom sizes e.g. 320w and would like to include additional sizes such as full, you can use wp_update_attachment_metadata( $attachment_id, $metadata );