Loop error on Qweb component template with Odoo17

Question

I'm stuck with a problem on Odoo17. I want to use the wizard on a project to display the main informations as the user_id or the order_lines that the project depends on. So to do that, maybe it's not the best way, I created a wizard (it works well), in the wizard view I added field that a javascript widget controls. That javascript call a with fetch controller that send back JSON data (it works well) to the javascript. Finally I display those data in a Qweb template. And here starts my problem : I can read some simple values but it cant read objects, don't know why. Here is my code :

controllers/project_infos.py

# -*- coding: utf-8 -*-
from odoo import http
from odoo.http import request
from itertools import groupby
import json
from operator import itemgetter

class MyWebController(http.Controller):
  @http.route('/addon/projet', auth='user', csrf=False )
  def my_controller_method(self, **kwargs):
      id = kwargs['id']
      project =request.env['project.project'].search([('id', '=', id)])
      clientId = project.partner_id
      client = request.env['res.partner'].search([('id', '=', clientId.id)])
      clientName =  client.name
      clientId = project.partner_id
      managerId = project.user_id
      saleId= project.sale_order_id
      
      projectTasks = request.env['project.task'].search([('project_id', '=',project.id), ('name', '=','Mise en facturation Complète')])
      manager = request.env['res.users'].search([('id', '=', managerId.id)])
      managerName = manager.name 
      
      client = request.env['res.partner'].search([('id', '=', clientId.id)])
      clientName =  client.name
      clientStreet =  client.street
      clientStreet2 =  client.street2
      clientZip= client.zip
      clientCity = client.city
    
      commande = request.env['sale.order'].search([('id', '=', saleId.id)])
      order_lines = request.env['sale.order.line'].search([('order_id','=',commande.id)])
      arr = []
      for line in order_lines :
          print (line.product_uom_qty)
          product = request.env['product.template'].search([('id', '=', line.product_template_id.id)])
          productCategory =  str(product.categ_id.name)
          productDescription = str(product.description_sale)
          print ()
          if productCategory != 'False':
            arr.append({"name":line.product_template_id.name, "desc":productDescription, 'cat':productCategory, 'qty':line.product_uom_qty})
      d = sorted(arr, key=itemgetter("cat"))
      grouped = {k: list(v) for k, v in groupby(d, itemgetter('cat'))}
      val = {
        'manager' : managerName,
        'name': clientName,
        'street': clientStreet,
        'street2': clientStreet2,
        'city' : clientCity,
        'zip': clientZip,
        'products':grouped
       }
      return json.dumps(val)
      

static/src/js/edit.js

/** @odoo-module */

import { standardFieldProps } from "@web/views/fields/standard_field_props";
import { registry } from "@web/core/registry";
const { Component, onWillStart, useState } = owl

export class Edit extends Component {
    setup() {
        this.state = useState({
            check: true
        })
        onWillStart(async () => {
            await this.projetInfos()
        })
    }
    async projetInfos() {
        var projectId = this.env.model.root.evalContext.context.id
        fetch('/addon/projet?id=' + projectId)
            .then(response => response.json())
            .then((data) => {
                var Format = []
                const result = (data['products'])
                Object.keys(result).map((d, index) => {
                    Format.push({ id: index, category: d, products: data['products'][d] })
                })
                //a simple string
                this.state.manager = data['manager']
                //an array of object
                this.state.products = Format
            })
    }
}
Edit.template = "addon.edit";
Edit.props = {
    ...standardFieldProps,
};
Edit.supportedTypes = ["char"];
export const activeField = { component: Edit };
registry.category("fields").add("edit", activeField);  

So everything is ok till then : I got all the data I want but when I want to display the state product which are nested objects Qweb tells me it's undefined.

static/src/xml/edit.xml

<?xml version="1.0" encoding="UTF-8"?>
<templates id="chart" xml:space="preserve">
    <t t-name="addon.edit" owl="1">
       <!-- ✅ Display the name of Manager -->
       <span>Manager :</span> <p t-esc='state.manager' />
       <!-- ❌ OwlError: Invalid loop expression: "undefined" is not iterable -->
       <t t-foreach="state.products" t-as="product" t-key="product.id">
        <p t-esc="product.category" />
       </t>
    </t>
</templates>

So I really don't know why I got this error. When I console.log the Format array, copy/paste it somewhere outside the fetch call in a state of my component, the Qweb loop works fine.

Somebody could help me ?

Thanks a lot in advance