partner-contact/partner_group/views/res_partner_views.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2018 Tecnativa - Sergio Teruel
     License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl). -->
<odoo>

    <record id="view_partner_form" model="ir.ui.view">
        <field name="name">Partner Group</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_partner_form"/>
        <field name="arch" type="xml">
            <field name="lang" position="after">
                <field name="group_id"/>
            </field>
        </field>
    </record>

    <record id="view_res_partner_filter" model="ir.ui.view">
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_res_partner_filter"/>
        <field name="arch" type="xml">
            <filter name="group_country" position="after">
                <filter name="group_group" string="Group" context="{'group_by': 'group_id'}"/>
            </filter>
            <field name="parent_id" position="after">
                <field name="group_id"/>
            </field>
        </field>
    </record>

</odoo>