data-protection/privacy_consent/data/ir_actions_server.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2018 Tecnativa - Jairo Llopis
     Copyright 2019 initOS GmbH - Florian Kantelberg
     License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl). -->

<data>

    <record id="update_opt_out" model="ir.actions.server">
        <field name="name">Update partner's opt out</field>
        <field name="model_id" ref="model_privacy_consent"/>
        <field name="crud_model_id" ref="base.model_res_partner"/>
        <field name="state">code</field>
        <field name="code">records.mapped('partner_id').write({'opt_out': not record.accepted})</field>
    </record>

</data>