mongoose: Timestamps are not being created

I’m trying to add timestamps to my nested objects, but it’s not working. Timestamps are being set only on the root documents (Church). Am I doing something wrong?

Here’s my schemas:

const churchSchema = new Schema({
	churchId: {
		type: Number,
		required: true,
	},
	integration: {
		type: Integration,
		required: true,
	},
	service: {
		type: Service,
		required: true,
	},
	events: {
		type: [ Event ],
		required: false,
	},
}, {
	timestamps: true,
});

const eventSchema = new Schema({
	churchId: {
		type: Number,
		required: true,
	},
	code: {
		type: String,
		required: true,
	},
	template: {
		type: Template,
		required: true,
	},
	users: {
		type: [ User ],
		required: false,
	},
	message: {
		type: Message,
		required: true,
	},
}, {
	timestamps: true,
}

const userSchema = new Schema({
	churchId: {
		type: Number,
		required: true,
	},
	email: {
		type: String,
		required: true,
	},
	fullname: {
		type: String,
		required: true,
	},
	dateOfBirth: {
		type: Date,
		required: true,
	},
	contacted: {
		type: Boolean,
		required: true,
		default: false,
	},
}, {
	timestamps: true,
});

Here’s the function I’m using to insert nested documents:

churchSchema.methods.addUserToEvent = async function (user, eventCode) {
	return await mongoose.model('Church').findOneAndUpdate({
		_id: this._id,
		events: {
			$elemMatch: {
				code: eventCode,
				users: {
					$not: {
						$elemMatch: {
							email: user.email,
						},
					},
				},
			},
		},
	}, {
		$addToSet: {
			'events.$.users': user,
		},
	}, {
		upsert: true,
		new: true,
		timestamps: true,
	});
};

MongoDB: 4.4.6 Mongoose: 5.13.2 Node.js: v14.17.0