Most efficient monolith structure to have an Express.js REST API with Next.js SSR client?

/project
|-- /node_modules
|-- /client
|-- /server
└- package.json

/project
|-- /node_modules
|-- /client
|-- /server
└- package.json

/project
|-- /client
|   |-- /node_modules
|   └- package.json
|-- /server
|   |-- /node_modules
└   └- package.json

/project
|-- /client
|   |-- /node_modules
|   └- package.json
|-- /server
|   |-- /node_modules
└   └- package.json

const app = express()

// Maybe run Next
app.get('/', (req, res) => {
  // Run Next SSR like...
  // res.send(next????)
})

app.get('/api', (req, res) => {
  res.status(200)
    .json({ resource: "value" })
})

app.listen(3000, () => "Express listening on port 3000")

const app = express()

// Maybe run Next
app.get('/', (req, res) => {
  // Run Next SSR like...
  // res.send(next????)
})

app.get('/api', (req, res) => {
  res.status(200)
    .json({ resource: "value" })
})

app.listen(3000, () => "Express listening on port 3000")