Hey @joemurrayaz. That configuration would work for something that handles routing, like an Express.js site. If your site is actually just HTML then this configuration is working as expected by only showing the home page.
If you go to the Source tab on the deployment details page, then toggle over to output, that will let you see which pages are included in the deployment and then paths to access them. Just make sure you remove the current rewrites configuration.
We have a list of other 404 debugging tips that can help you solve this.
But if you need more help, please share your public repo or a minimal reproducible example so we can work together from the same code to find the best solution for you