oca-technical/odoo-bringout-oca-hr-hr_employee_firstname/hr_employee_firstname/views/hr_view.xml

<?xml version="1.0" encoding="utf-8" ?>
<odoo>
    <record id="view_employee_form" model="ir.ui.view">
        <field name="model">hr.employee</field>
        <field name="inherit_id" ref="hr.view_employee_form" />
        <field name="arch" type="xml">
            <xpath expr="//field[@name='name']" position="attributes">
                <attribute name="readonly">1</attribute>
                <attribute name="no_label">1</attribute>
                <attribute name="required">0</attribute>
            </xpath>
            <xpath expr="//h1//field[@name='name']/.." position="after">
                <group>
                    <field
                        name="lastname"
                        attrs="{'required': [('firstname', '=', False)]}"
                    />
                    <field
                        name="firstname"
                        attrs="{'required': [('lastname', '=', False)]}"
                    />
                </group>
            </xpath>
        </field>
    </record>
</odoo>