When you create a new ad in Ads Manager, Facebook generates a new page post. This post has a unique reference number – post ID.
If you duplicate an ad, Facebook will create a new post again. Even if these posts are identical – same visual, link, copy, etc. While it is technically a new post, it will not have any comments, likes, and shares, that the original one had.
To keep all engagement – so called social proof – you can link your new ad to the same post. This means that instead of creating a new duplicate post, your ad will lead to the existing post.