Jest mockImplementation is not a function

I have this simplified Jest test:

import login from "../../src/controller/auth/login";
import findUserByEmail from "../../src/api/db/find-user-by-email";

jest.mock("../../src/api/db/find-user-by-email");
const mockedfindUserByEmail = findUserByEmail as jest.Mocked<typeof findUserByEmail>;

describe("Login API", () => {
  test('should return 401', async () => {

    const req = {
      email: "email@domain.com",
      password: "password"
    };

    mockedfindUserByEmail.mockImplementation(async () => false)

    expect(await login(req).status).toBe(401);
  });
});

I got this mock from the docs. When I don't mock the test works fine because the login module connects to the database. But when I use the above mock I get:

TypeError: findUserByEmail.mockImplementation is not a function

Can you help?

The find-user-by-email file:

import { User } from "../../entities/main/user";
const db: any = require("../../db/models");

export default async (email: string)
  : Promise<User> => {
  return await db.user.findOne({
    where: { email },
    raw: true,
  });
};