SSG + CSR is not supported in App Router

[owareoro]

Goals

1. Render a website as SSG
2. Prerender dynamic parameters known at build time
3. Allow client-side handling for dynamic parameters

Non-Goals

Background

Nextjs claims to support every deployment mode.
However, there is something which works out of the box with React Router and Tanstack Start is not supported on NextJs for unknown reasons.
When attempting to implement this on Nextjs - I ran into two conflicting errors.

[Error: Page "/products/view-product/[productSlug]/page" cannot use both "use client" and export function "generateStaticParams()".] {
  type: 'Error'
}
[Error: Page "/products/view-product/[productSlug]" is missing "generateStaticParams()" so it cannot be used with "output: export" config.]

Proposal

I believe the Pages Router supports this at least in development. So, in a way, this is a bit of a regression.
For now, the only way to work around this is to move to the less familiar React Router which I have done.

But that means I have to lose out on all the other NextJs features that like automatic image optimization as well as other features should I eventually decide SSR is the better strategy.