whatsapp_web_groups/cutom_report_invoice/models/account_move.py

from odoo import models, fields


class AccountMove(models.Model):
    _inherit = "account.move"

    rate = fields.Float(compute="_get_last_exchannge_rate")

    def _get_last_exchannge_rate(self):
        rate = self.currency_id.rate_ids[0]
        if rate:
            self.rate= rate.inverse_company_rate