partner-contact/partner_contact_department/views/res_partner_view.xml

<?xml version="1.0" encoding="utf-8" ?>
<flectra>
    <record model="ir.ui.view" id="view_partner_form_department">
        <field name="name">Partner form with department</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_partner_form" />
        <field name="arch" type="xml">
            <xpath expr="//sheet/group//field[@name='function']" position="after">
                <field
                    name="department_id"
                    placeholder="Department"
                    invisible="is_company"
                    options='{"no_open": True}'
                />
            </xpath>
            <xpath
                expr="//field[@name='child_ids']/form//field[@name='function']"
                position="after"
            >
                <field name="is_company" invisible="True" />
                <field
                    name="department_id"
                    placeholder="Department"
                    invisible="is_company"
                    options='{"no_open": True}'
                />
            </xpath>
        </field>
    </record>
    <record model="ir.ui.view" id="view_res_partner_filter_department">
        <field name="name">Partner search with department</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_res_partner_filter" />
        <field name="arch" type="xml">
            <field name="category_id" position="after">
                <field name="department_id" />
            </field>
            <filter name="salesperson" position="after">
                <filter
                    name="department"
                    string="Department"
                    domain="[('is_company', '=', False)]"
                    context="{'group_by': 'department_id'}"
                />
            </filter>
        </field>
    </record>
</flectra>