Populate is returning empty array

I'm trying to populate the User in Project data

**Model from User **

const { Schema, model } = require('mongoose')

const UserSchema = new Schema({
    name: {
        type: String,
        required: true,
    },
    lName: {
        type: String,
        required: true,
    },
    email: {
        type: String,
        required: true,
    },
    password: {
        type: String,
        required: true,
    },
    create_at: {
        type: Date,
        default: Date.now
    }

})
UserSchema.methods.toJSON = function () {
    let users = this;
    let userObject = users.toObject();
    delete userObject.password;
    return userObject;
}

module.exports = model('User', UserSchema)

**Model from Project **

const { Schema, model } = require('mongoose');
const User = require('./user')

const projectSchema = new Schema({
    user: [{
        type: Schema.Types.ObjectId,
        ref: 'User',
    }],
    name: {
        type: String,
        required: true,
    },
    description: {
        type: String,
        required: true,
    },
    category: {
        type: String,
    },
    lang: {
        type: String,
        required: true,
    },
    date: {
        type: Date,
        required: true,
    },
    image: {
        type: String,
    }

}, {
    timestamps: true,
})

module.exports = model('Project', projectSchema)

**Controller from Project **

const Project = require('../models/project');
const User = require('../models/user');

const createProject = (req, res) => {
    let body = req.body;
    let userIdentity = req.user

    let project = new Project(body);

    project.save()
        .then((projectDB) => {
            if (!projectDB) return res.status(400).send({
                status: 'error',
                message: 'Project already exists'
            })
            return res.status(200).send({
                status: 'success',
                userIdentity,
                project: projectDB
            })
        })

}

const getProjects = (req, res) => {
    Project.find()
        .populate('user', "-\__v")
        .then((projectDB) => {
            if (!projectDB) return res.status(400).send({
                status: 'error',
                message: 'Project not found'
            })
            return res.status(200).send({
                status: 'success',
                projects: projectDB
            })
        }).catch((err) => {
            return res.status(500).send({
                status: 'error',
                error: err.message
            })
        })
}

const getOneProject = async (req, res) => {
    let projectId = req.params.id

    await Project.findOne({ _id: projectId })
        .populate('user', "-__v")
        .then((projectDB) => {
            if (!projectDB) return res.status(400).send({
                status: 'error',
                message: 'Project not found'
            })
            return res.status(200).send({
                status: 'success',
                projects: projectDB
            })
        })
        .catch((err) => {
            return res.status(500).send({
                status: 'error',
                error: err.message
            })
        });

}

module.exports = {
    createProject,
    getProjects,
    getOneProject
}

Response Like i've said. the .populate is returning an empty array

I have 4 days trying to solve this problem i've tried .populate({path: 'user'})
with exec or execPopulate

i've tried many solutions and i have the same result

i hope someone could help me