@Jimb0 You’re asking for help to get a Next.js based site to work on GitHub Pages.
This forum is for Netlify and their products/services.
GitHub Pages is a product of GitHub.
Next.js is a product of Vercel.
Netlify doesn’t run Github Pages nor do they produce Next.js.
Since your request for assistance doesn’t involve Netlify it would be better to ask the support of one of the companies/communities that are involved, so at Vercel, GitHub Pages, or even somewhere generic like Stack Overflow.