Can't populate field with ObjectId in mongoose

Question

I'm learning React for a couple of months now and I struggle to populate some fields with mongoose I got a Projects and a User collection and each Project have a creator and a team of Users.

createdBy is a single ObjectId and participants is an array of objects containing the user.ObjectId and other fields related to the project.

Here's the clg of a project structure

{
  _id: new ObjectId('65b518c381cfb1bec92fe0b9'),
  title: 'Project 0',
  createdBy: new ObjectId('65aabac39125371ade73ddf0'),
  brief: 'Du blabla, plein de blabla',
  deadline: 2024-03-20T18:00:00.245Z,
  participants: [
    {
      _id: new ObjectId('65c241ed2d462330785bb2e4'),
      accessLVL: 'lead',
      joinDate: 2024-01-27T17:09:07.245Z,
      userID: new ObjectId('65aabac39125371ade73ddf0')
    },
    {
      _id: new ObjectId('65c241ed2d462330785bb2e5'),
      accessLVL: 'member',
      joinDate: 2024-01-27T17:09:07.245Z,
      userID: new ObjectId('65aabac39125371ade73ddf4')
    },
    {
      _id: new ObjectId('65c241ed2d462330785bb2e6'),
      accessLVL: 'member',
      joinDate: 2024-01-27T17:09:07.245Z,
      userID: new ObjectId('65aabac39125371ade73ddf2')
    }
  ],
  submits: [
    {
      _id: new ObjectId('65c241ed2d462330785bb2e2'),
      submitImage: [Array],
      userId: new ObjectId('65aabac39125371ade73ddf4'),
      update: 1999-12-31T23:00:00.000Z,
      callback: [Array]
    }
  ],
}

In my schemas, everything seems ok (Schema.Types.ObjectId and the ref to the user schema)

const ProjectSchema = new Schema(
  { title: String,
    createdBy: {
      type: mongoose.Schema.Types.ObjectId, ref: "User", require:true, 
      min: 2,
      max: 100,
    },
    createdAt: {
      type: Date,
      required: true,
      max: 50,
      unique: true,
    },
    participants: [{
        userID: {type: mongoose.Schema.Types.ObjectId, ref: "User", require:true}, 
        accessLVL: {
            type: String,
            enum: ["member", "lead", "guest"],
            default: "member",
          },
        joinDate: Date,
    }],
    deadline: Date,
    brief: String,
    submits: [{
      userID: {type: mongoose.Schema.Types.ObjectId, ref: "User", require:true},
      submitImage: [String],
      update: Date,
      callback: [{
            userID: {type: mongoose.Schema.Types.ObjectId, ref: "User", require:true},
            callback: String,
            majDate: Date,
      }],
    }],
    close: Boolean,
    closeDate: Date, 
},
{ timestamps: true }
);

const UserSchema = new Schema(
  {id: {
    type: String
  },
  avatar: {
    type: String,
    required: true,
    max: 100,
  },
  name: {
    type: String,
    required: true,
    min: 2,
    max: 100,
  },
  email: {
    type: String,
    required: true,
    max: 50,
    unique: true,
    lowercase: true,
    index: true,
  },
  password: {
    type: String,
    required: true,
    min: 5,
  },
  affiliate: {
    type: String,
    required: true,
    min: 5,
  },
  contact: {
    type:String,
    max: 20,
  },
  ongoing: [{
      type: mongoose.Schema.Types.ObjectId, 
      ref: "Project",
  }],
  occupation: {
    type: String,
    max: 30,
  },
  status: {
    type: String,
    enum: ["team", "client"],
    default: "team",
  },
  privilege: {
    type: String,
    enum: ["user", "manager", "admin"],
    default: "user",
  },
  registerDate: Date,
  lastSeen: Date,
  
},
{ timestamps: true }
);

But when I try to populate createdBy or participants.userID it return thoses fields as null

Here's the query

const fetchProjects = async (req, res) => {
    try {
    const projects = await Project.find().populate("createdBy");
    console.log(projects[0]);
    res.json({projects});
    } catch(err) {
        return res.sendStatus(404);
    }
}

and the clg of the result

  _id: new ObjectId('65b518c381cfb1bec92fe0b9'),
  title: 'Project 0',
  createdBy: null,
  brief: 'Du blabla, plein de blabla',
...

I tried every populate method I found

Project.find().populate("createdBy")

and

Project.find().populate({path:"createdBy", model:"User"})

even with Project.find({}) like I saw somewhere but always the same createdBy: null, result. I'm surely messing something but I can't find what yet. Any advices ?