Apologies for the late reply, I hadn't seen a response come through.
Managed to resolve this issue not long after posting. The issue was with the next.config.mjs file and I've simplified the approach based on a GitHub application we were linked to by a person at Prismic.
Out of curiosity, is there a plan for the Developer documentation to be updated to support NextJS 14 and more specifically the App Router as everything right now points at the Page Router?