Issues with finding a specific user in a reference array in mongodb/mongoose

Question

I'm having issues with finding a specific user in a reference array, I have an Activity schema which as an array of participants that references a User Schema.

I've been trying using something like this:

(userid is a variable has the specified user id)

activityQuery = Activity.find({participants: userid});

it does not return anything.

Example of the data in the db:

Data example Image

Here are the used schemas:

Activity Model

const mongoose = require("mongoose");
const uniqueValidator = require("mongoose-unique-validator");

const activitySchema = mongoose.Schema({
  image: { type: String, required: true },
  content: { type: String, required: true },
  title: { type: String, required: true },
  numberOfParticipants: { type: Number, required: true },
  state: { type: String, required: true },
  date: { type: Date, required: true },
  participants: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: "User",
    },
  ],
  areasOfInterest: [
    {
      type: String,
      required: true,
    },
  ],
  inquiries: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: "Inquiry",
    },
  ],
  proposalId: {
    type: mongoose.Schema.Types.ObjectId,
    ref: "Proposal",
  },
});

activitySchema.plugin(uniqueValidator);

module.exports = mongoose.model("Activity", activitySchema);

User Model

const mongoose = require("mongoose");
const uniqueValidator = require("mongoose-unique-validator");

const userSchema = mongoose.Schema({
  email: { type: String, required: true, unique: true },
  password: { type: String, required: true },
  userType: { type: String, required: true },
  birthdate: { type: Date },
  name: { type: String, required: true },
  state: { type: String, required: true },
  profileImage: { type: String },
  gender: { type: String },
  address: { type: String },
  website: { type: String },
  accountableName: { type: String },
  areasOfInterest: [
    {
      type: String,
    },
  ],
  activities: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: "Activity",
    },
  ],
  member: { type: String },
  obs: { type: String },
  reasons: [{ type: String }],
  formation: { type: String },
  school: { type: String },
  phone: { type: String },
  familyMembers: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: "FamilyMember",
    },
  ],
  photos: [{ type: String }],
  joinDate: { type: Date },
});

userSchema.plugin(uniqueValidator);

module.exports = mongoose.model("User", userSchema);