This line causes the built JS file to contain this first line:

import { jsxs, jsx, Fragment } from 'react/jsx-runtime';

This causes the following fatal browser error when serving the built preview app:

Uncaught TypeError: Failed to resolve module specifier "react/jsx-runtime". Relative references must start with either "/", "./", or "../".

This seems too deliberate to be a bug, am I missing something obvious?