This new site was built using Statamic CMS. Statamic is a flat file CMS.
I initially created a version of this site using a combination React, Nx, Styled Components and MDX. Long story short, for me, that became complicated and over engineered really quickly.
The simplicity, flexibility and features of Statamic made it easy to get a basic version of this site, with a little help from Tailwind CSS, in a few hours.