social/mail_activity_partner/views/mail_activity_views.xml

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

    <!-- FORM VIEW -->
    <record id="mail_activity_view_form_board" model="ir.ui.view">
        <field name="name">mail.activity.boards.view.form</field>
        <field name="model">mail.activity</field>
        <field
            name="inherit_id"
            ref="mail_activity_board.mail_activity_view_form_board"
        />
        <field name="arch" type="xml">
            <field name="activity_type_id" position="before">
                <field name="partner_id" readonly="True" />
                <field name="commercial_partner_id" />
            </field>
        </field>
    </record>


    <!-- TREE VIEW -->
    <record id="mail_activity_view_tree" model="ir.ui.view">
        <field name="name">mail.activity.boards.view.tree</field>
        <field name="model">mail.activity</field>
        <field name="inherit_id" ref="mail_activity_board.mail_activity_view_tree" />
        <field name="arch" type="xml">
            <field name="activity_type_id" position="before">
                <field name="partner_id" readonly="True" />
                <field name="commercial_partner_id" />
            </field>
        </field>
    </record>


    <!-- KANBAN VIEW -->
     <record id="mail_activity_view_kanban" model="ir.ui.view">
         <field name="name">mail.activity.boards.view.kanban</field>
         <field name="model">mail.activity</field>
         <field name="inherit_id" ref="mail_activity_board.mail_activity_view_kanban" />
         <field name="arch" type="xml">
             <strong class="o_kanban_record_title" position="inside">
                 <field name="partner_id" />
             </strong>
         </field>
    </record>


    <!-- SEARCH VIEW -->
    <record id="mail_activity_view_search" model="ir.ui.view">
        <field name="name">mail.activity.boards.view.search</field>
        <field name="model">mail.activity</field>
        <field name="inherit_id" ref="mail_activity_board.mail_activity_view_search" />
        <field name="arch" type="xml">
            <xpath expr='//field[@name="res_model_id"]' position='before'>
                <field name="partner_id" />
                <field name="commercial_partner_id" />
            </xpath>
        </field>
    </record>

</odoo>