Eventually, the only issue was that the Vite configuration section I added was in the wrong place.

So now I had at lib vite.config:

rollupOptions: {
        external: ['react', 'react-dom'],
}

and in app layer vite.config:

 resolve: {
      dedupe: ['react', 'react-dom', '@emotion/react', '@emotion/styled', '@mui/material', '@mui/system'],
 },

That's a working configuration for me