Confusion in Query API of mongoose

Can anyone please tell me why the given below code(PART-1) works fine whereas gives error that posts.skip is not a function? in PART-2
I am wondering that why in PART-1 code it returned Query instance whereas I am getting an array of posts.

PART-1
const query = MyModel.find(); // `query` is an instance of `Query`
query.setOptions({ lean : true });
query.collection(MyModel.collection);
query.where('age').gte(21).exec(callback);

PART-2
const posts = await PostModel.find({});
posts.skip((page - 1) * 10).limit(10);

Basically I am trying to refactor this code so that I don't have to each time use pagination logic and achieve that by writing a pagination util function where the function will have first params a Query instance of mongoose

 getAllPost: async (req, res, next) => {
    const pagination = req.query.pagination ? parseInt(req.query.pagination) : 10
    const currentPage = req.query.page ? parseInt(req.query.page) : 1
    try {
      const posts = await PostModel.find({}).lean()
        .skip((currentPage - 1) * pagination)
        .limit(pagination)
        .populate('userId', ['name.firstName', 'name.lastName', 'email', 'isAdmin'])
        .sort({ updatedAt: -1 })
        .exec()
      if (!posts.length) {
        return res.status(HttpStatus.NOT_FOUND).json({ message: 'No posts found' })
      }
      return res.status(HttpStatus.OK).json({ posts: posts })
    } catch (error) {
      HANDLER.handleError(res, error)
    }
  },

Util function like: (For example)

module.exports = {
  paginate: async (req, query, next) => {
    const options= {
      pagination: req.query.pagination ? parseInt(req.query.pagination) : 10,
      currentPage: req.query.page ? parseInt(req.query.page) : 1
    }
    query.skip((currentPage-1)*pagination).limit(pagination)
    query.exec((err, result)=>{ return result; })
  }
}