account-financial-tools/account_bank_statement_chatter/views/account_bank_statement_views.xml

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

    <record id="view_bank_statement_form" model="ir.ui.view">
        <field name="model">account.bank.statement</field>
        <field name="inherit_id" ref="account.view_bank_statement_form"/>
        <field name="arch" type="xml">
            <sheet position="after">
                <div class="oe_chatter">
                    <field name="message_follower_ids" widget="mail_followers"/>
                    <field name="activity_ids" widget="mail_activity"/>
                    <field name="message_ids" widget="mail_thread"/>
                </div>
            </sheet>
        </field>
    </record>

</odoo>