suite/project_task_line/views/project_views.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
    <record id="view_task_form2_inherit" model="ir.ui.view">
        <field name="name">project.task.form.inherit</field>
        <field name="model">project.task</field>
        <field name="inherit_id" ref="project.view_task_form2" />
        <field name="arch" type="xml">
            <xpath expr="//div[@name='button_box']" position="inside">
                <button name="action_subtask" type="object" class="oe_stat_button" icon="fa-tasks" attrs="{'invisible' : ['|', ('allow_subtasks', '=', False), ('id', '=', False)]}" context="{'default_user_ids': user_ids, 'default_parent_id': id, 'default_project_id': project_id}">
                    <span class="o_stat_value"><field name="subtask_count_done" widget="statinfo" nolabel="1"/> / <field name="subtask_count" widget="statinfo" nolabel="1"/></span>
                    <span class="o_stat_text">Sub-Tasks</span>
                </button>
            </xpath>
            <xpath expr="//page[@name='description_page']" position="after">
                <page name="task_lines" string="Todo List">
                    <field name="line_ids" widget="one2many_list" context="{'default_task_id': id}">
                        <tree editable="bottom">
                            <field name="sequence" widget="handle"/>
                            <field name="name"/>
                            <field name="kanban_state" widget="selection" string="Status"/>
                            <field name="user_id" string="Completed by" options="{'no_create': True, 'no_create_edit': True, 'no_open': True}"/>
                        </tree>
                    </field>
                </page>
            </xpath>
        </field>
    </record>
</odoo>