[REM] I have not been able to debug even if I thing I am very close to make it work

project_timesheet_matrix/__init__.py

@@ -0,0 +1,2 @@
+from . import wizard
+from . import models

project_timesheet_matrix/__manifest__.py

@@ -0,0 +1,18 @@
+{
+    'name': 'Project Timesheet Matrix',
+    'summary': "Wizard which allows to timesheet per user per day of a month for a project",
+    "version": "1.0.0",
+    "author": "JMDN Solutions Sàrl",
+    "website": "https://www.jmdn-group.com",
+    "license": "AGPL-3",
+    "category": "Project",
+    "depends": [
+        'web_widget_x2many_2d_matrix', 'project', 'analytic'
+    ],
+    "data": [
+        # 'security/ir.model.access.csv',
+        'views/project_timesheet_matrix_view.xml',
+        'wizard/project_timesheet_matrix_wiz.xml',
+    ],
+    "installable": True,
+}

project_timesheet_matrix/models/__init__.py

@@ -0,0 +1 @@
+from . import project_project

project_timesheet_matrix/models/project_project.py

@@ -0,0 +1,20 @@
+from odoo import models, fields, api
+
+
+class ProjectProject(models.Model):
+    _inherit = "project.project"
+
+    @api.model
+    def open_timesheets_matrix(self):
+        import pdb; pdb.set_trace()
+        wiz = self.env['project.timesheet.matrix.wiz'].create({})
+        return {
+            'name': 'Edit timesheets',
+            'type': 'ir.actions.act_window',
+            'view_type': 'form',
+            'view_mode': 'form',
+            'res_model': 'project.timesheet.matrix.wiz',
+            'target': 'new',
+            'res_id': wiz.id,
+            'context': self.env.context,
+        }

project_timesheet_matrix/views/project_timesheet_matrix_view.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<odoo>
+    <record id="project_timesheet_matrix_view_form" model="ir.ui.view">
+        <field name="name">project.timesheet.matrix.view.form</field>
+        <field name="model">project.project</field>
+        <field name="inherit_id" ref="project.view_project_kanban"/>
+        <field name="arch" type="xml">
+            <xpath expr="//div[hasclass('o_kanban_card_manage_section')]" position="inside">
+                <div>
+                    <!-- <a name="open_timesheets_matrix" type="object">Timesheet</a> -->
+                    <button name="open_timesheets_matrix" type="object" string="Workers" class="oe_stat_button" icon="fa-edit" />                    
+                </div>
+            </xpath>
+            <!-- <field name="task_count" position="after">
+                <button name="open_project_timesheet_matrix" type="object" string="Timesheet Workers" class="oe_stat_button" icon="fa-edit" />
+            </field> -->
+        </field>
+    </record>
+</odoo>

project_timesheet_matrix/wizard/__init__.py

@@ -0,0 +1 @@
+from . import project_timesheet_matrix_wiz

project_timesheet_matrix/wizard/project_timesheet_matrix_wiz.py

@@ -0,0 +1,24 @@
+from odoo import fields, models
+
+class ProjectTimesheetMatrixWizard(models.TransientModel):
+    _name = 'project.timesheet.matrix.wiz'
+
+    def _default_line_ids(self):
+        import pdb; pdb.set_trace()
+        recs = self.env['account.analytic.account'].search([])
+        users = self.env['account.analytic.line'].search([]).mapped('user_id')
+
+        return [
+            (0, 0, {
+                'name': "{}'s task on {}".format(usr.name, rec.name),
+                'account_id': rec.id,
+                'user_id': usr.id,
+                'unit_amount': 0,
+            })
+            if not rec.line_ids.filtered(lambda x:x.user_id == usr) else
+            (4, rec.line_ids.filtered(lambda x:x.user_id == usr)[0].id)
+            for rec in recs
+            for usr in users
+        ]
+    
+    line_ids = fields.Many2many('account.analytic.line', default=_default_line_ids)

project_timesheet_matrix/wizard/project_timesheet_matrix_wiz.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo>
+
+  <record id="project_timesheet_matrix_wiz" model="ir.ui.view">
+    <field name="name">project.timesheet.matrix.wiz</field>
+    <field name="model">project.timesheet.matrix.wiz</field>
+    <field name="type">form</field>
+    <field name="arch" type="xml">
+      <form>
+        <field name="line_ids" widget="x2many_2d_matrix" field_x_axis="account_id" field_y_axis="user_id" field_value="unit_amount">
+          <tree>
+            <field name="account_id"/>
+            <field name="user_id"/>
+            <field name="unit_amount"/>
+          </tree>
+        </field>
+      </form>
+    </field>
+  </record>
+
+</odoo>