I have added a custom module which should change the attribute from hide to show. But no change is made. If I click on it directly via the list, then it works.

<record id="mymodule_crm_lead_search_opportunity" model="ir.ui.view">
            <field name="name">mymodule.crm.lead.search.opportunity</field>
            <field name="model">crm.lead</field>            
            <field name="inherit_id" ref="crm.crm_case_tree_view_oppor"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='activity_ids']" position="attributes">
                    <attribute name="optional">show</attribute>
                </xpath>
            </field>
        </record>