Hi,

1. Create a new XML file.

<odoo>
  <record id="sale_invoice_action" model="ir.actions.act_window">
  <field name="name">Invoice</field>
<field name="res_model">account.move</field>
<field name="view_mode">tree,form</field>
<field name="domain">[('move_type','=','out_invoice')]</field>
<field name="context">{'default_move_type': 'out_invoice'}</field>
</record>
<menuitem id="menu_sale_invoice_main" name="Invoice" action="sale_invoice_action" parent="sale.sale_order_menu" sequence="20"/>
</odoo>

Hope it helps

Please watch the reference video of creating menu in Odoo..