partner-contact/partner_multi_relation/views/res_partner.xml

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

        <record id="view_res_partner_filter" model="ir.ui.view">
            <field name="name">partner_multi_relation.view_partner_filter</field>
            <field name="inherit_id" ref="base.view_res_partner_filter" />
            <field name="model">res.partner</field>
            <field type="xml" name="arch">
                <data>
                    <field name="parent_id" position="after">
                        <field name="search_relation_partner_id" />
                        <field name="search_relation_type_id" />
                        <field name="search_relation_date" />
                        <field name="search_relation_partner_category_id" />
                    </field>
                </data>
            </field>
        </record>

        <record id="view_partner_form" model="ir.ui.view">
            <field name="name">partner_multi_relation.view_partner_form</field>
            <field name="inherit_id" ref="base.view_partner_form" />
            <field name="model">res.partner</field>
            <field type="xml" name="arch">
                <xpath expr="//div[@name='button_box']" position="inside">
                    <button
                        class="oe_inline oe_stat_button"
                        type="action"
                        context="{
                            'search_default_this_partner_id': active_id,
                            'default_this_partner_id': active_id,
                            'active_model': 'res.partner',
                            'active_id': id,
                            'active_ids': [id],
                            'active_test': False,
                        }"
                        name="%(action_res_partner_relation_all)d"
                        icon="fa-users"
                        >
                        <field
                            string="Relations"
                            name="relation_count"
                            widget="statinfo"
                            />
                    </button>
                </xpath>
            </field>
        </record>

        <act_window id="action_show_partner_multi_relation"
            name="Show partner's relations"
            src_model="res.partner"
            res_model="res.partner.relation.all"
            domain="[('this_partner_id', 'in', active_ids)]"
            key2="client_action_multi" />

</odoo>