partner-contact/partner_company_group/views/contact_view.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
    <record id="view_partner_form" model="ir.ui.view">
        <field name="name">res.partner.form</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_partner_form" />
        <field name="arch" type="xml">
            <field name="vat" position="before">
                <field
                    name="company_group_id"
                    attrs="{'invisible': [('is_company','=', False)]}"
                />
            </field>
        </field>
    </record>
    <record id="view_res_partner_filter" model="ir.ui.view">
        <field name="name">res.partner.select</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_res_partner_filter" />
        <field name="arch" type="xml">
            <field name="name" position="after">
                <field name="company_group_id" />
            </field>
            <filter name="group_company" position="before">
                <filter
                    name="group_company_group"
                    string="Company Group"
                    context="{'group_by': 'company_group_id'}"
                />
            </filter>
        </field>
    </record>
    <record id="action_open_group_members" model="ir.actions.act_window">
        <field name="name">Company group members</field>
        <field name="res_model">res.partner</field>
        <field name="binding_model_id" ref="model_res_partner" />
        <field name="view_mode">tree</field>
        <field name="target">current</field>
        <field
            name="domain"
        >[('company_group_id', 'in', context.get('active_ids'))]</field>
    </record>
</odoo>