Previous/Next Product

We are using a them that didn’t have any Pagination associated with it so have developed some local code, which seems to work.
… apart from the Previous/Next products are not the expected ones i.e. the products in each category are displayed alphabetically by product name/code whereas the Pagination appears to identify Previous and Next by reference by the date they were created.

So the question is, how do we set the order for Previous/Next to Product Name/Code alphabetic?

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