Jest mockImplementation is not a function but works with require

I'm writing a test using jest and TS and I want to mock a function from a module, with two different implementations for two tests, although when using import I have an error saying mockImplementation is not a function

BUT, if I import the module with require, everything works. Can someone explain me why?

The snippet below works, but if I change the require to import { execSync } from 'child_process' the error appears

jest.mock('child_process', () => {
  return {
    execSync: jest.fn(),
  };
});

const packageToMock = require('child_process');

packageToMock.execSync.mockImplementation(() => {
      return something
 });

Also could I have this mock behaviour with spyOn? how?