in node.js ESM I want to stub an exported module thats the default

I have a very simple auth middleware with an export default () anonymous function:

export default () => async (req, res, next) => {
  try {
       // some auth implementation... does not matter
    } else {
      throw new Error('No "Bearer" token passed as header')
    }

    next()
  } catch (err) {
    next(err)
  }
}

I want to stub this in my unit tests to just continue with next().

import express from 'express';
import supertest from 'supertest';
import { router } from "express-file-routing"
import auth from '../../middlewares/auth.js';
import sinon from 'sinon'

describe("/foo", () => {
    let app, request;
    
    before(async () => {
        app = express();
        app.use("/", await router())
        request = supertest(app);
    });

    beforeEach(() => {
   
        sinon.stub(auth()).callsFake((req, res, next) => next());
        // tried also ...
        // sinon.replace(auth, 'default', () => (req, res, next) => next());
});
//... test continue

But these are not working. I am getting TypeError: sinon.stub(...).callsFake is not a function
or
TypeError: Cannot replace non-existent property default. Perhaps you meant sandbox.define()? when I try with sinon.replace