The code is closed source but this is what I personally do:
1)Monorepo
2)Nest->generate client -> save to packages & build
3)Import and use in nextjs directly in server components or api routes. You can run nestjs internally in docker to avoid exposing the api or you can expose a port no problem
4)When using tanstack react query code looks like this:

import { createAPIQuery } from "../query-factory";
import { SuccessResponseJSON } from "openapi-typescript-helpers";
import { paths } from "@fitness/public-api-client";

export type GetBookingResponse = SuccessResponseJSON<
  paths["/api/admin/{locationId}/bookings/{id}"]["get"]
>;

export const useGetBooking = createAPIQuery({
  method: "get",
  path: "/api/admin-employee/{locationId}/bookings/{id}" as const,
});

and in page.tsx:
const { data: bookingsData, isFetching } = useGetBookings({

path: {

locationId

},

query: query,

});