Not sure why this was voted down specifically. Other than not using/mentioning `react-dom-server`[1]
Will mention that React rendering server-side can be slow and problematic. And should generally be limited to *ONLY* when SSO will be needed and effective. Google and Bing will both do client-side rendering as long as your routing is configured properly.
With some caching (depends on usage and again can be more complicated), you could do certain doughnut caching where only some modules are server-rendered and shared cached results. (Walmart did a lot of work towards this)
In general, it may have been easier to port the app to Next.js or similar, which would have been a little more consistent with the broader community.
[1] https://reactjs.org/docs/react-dom-server.html