React4xp works by having Enonic XP serving XP-rendered HTML and JS assets that are react apps (“entries”) that run in the browser as regular react. Server-side rendered react apps should be no different; only that a representation of the react app is rendered with the HTML and then activated in the browser with
React.hydrate. So in principle, this should work (although I’ve never tested with react router).
How does this error behave - ie. are you getting any messages in the browser console, or from XP in the server log?