Mongoose subdocument update: dot notation assignment OR .findByIdAndUpdate()

Question

I have a server setup with nodejs/express and I'm also using mongodb and mongoose. I was following some tutorials and adapting to my project which is basically an user database for a web app. The thing is, when updating a property of my document User I'm using two different ways to do so: one by a dot notation + assignment and the other using the mongoose model method findByIdAndUpdate().

I've searched for other questions and I just found different questions here and here using these solutions but I couldn't find any comparison as to when should I use one instead of the other, can someone explains this, please?

My model schema:

const mongoose = require('../../db');

const UserSchema = new mongoose.Schema({
    username: {
        type: String,
        required: true,
    },
    email: {
        type: String,
        unique: true,
        required: true,
        lowercase: true,
    },
    password: {
        type: String,
        required: true,
        select: false,

    },
    score: {
        type: Number,
        required: true,
        default: 0
    },
    authToken: {
        type: String,
        select: false
    },
    authTokenExpires: {
        type: Date,
        select: false
    },
    passwordResetToken: {
        type: String,
        select: false
    },
    passwordResetTokenExpires: {
        type: Date,
        select: false
    },
    createdAt: {
        type: Date,
        default: Date.now,
    },
});

A request I'm using to "forgot password" case in which I supply a resetPassword token (using .findByIdandUpdate()):

const express = require('express');
const User = require('../models/User');
const router = express.Router();

router.post('/forgot_password', async (req, res) => {
    const { email } = req.body;
    const user = await User.findOne({ email }).select('+password');

    try {
        await User.findByIdAndUpdate(user._id, { //First way of updating document 
            '$set': {
                passwordResetToken: token,
                passwordResetExpires: now,
            }
        });
    catch (err) {
        return res.status(400).json({ error: 'Recover password process failed. Please try again' })
    }
});

And here it's another request to actually reset the password (using dot notation assignment):

const express = require('express');
const User = require('../models/User');
const router = express.Router();

router.post('/reset_password', async (req, res) => {
    const { email, token, password } = req.body;
    const user = await User.findOne({ email }).select('+passwordResetToken passwordResetTokenExpires');

    try {
        const now = new Date();

        if (now > user.passwordResetExpires) {
            return res.status(400).json({ error: 'Token expired, please generate a new token' })
        }

        user.password = password; //Second way of updating document
        user.passwordResetExpires = null;
        await user.save();

        return res.send();
    }
    catch (err) {
        console.log(err)
        return res.status(400).json({ error: 'Reset password process failed. Please try again' })
    }
});