odoo16/addons/sale_project/views/sale_project_portal_templates.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <template id="portal_tasks_list_inherit" inherit_id="project.portal_tasks_list">
        <xpath expr="//t[@t-foreach='grouped_tasks']/tbody/tr[hasclass('table-light')]" position="inside">
            <th t-if="groupby == 'sale_order'" t-attf-colspan="{{grouped_tasks_colspan}}">
                <span t-if="tasks[0].sudo().sale_order_id" class="text-truncate" t-field="tasks[0].sudo().sale_order_id"/>
                <span t-else="">No Sales Order</span>
            </th>
            <th t-if="groupby == 'sale_line'" t-attf-colspan="{{grouped_tasks_colspan}}">
                <span t-if="tasks[0].sudo().sale_line_id" class="text-truncate" t-field="tasks[0].sudo().sale_line_id"/>
                <span t-else="">No Sales Order Item</span>
            </th>
        </xpath>
    </template>

</odoo>