Hi,

create a new module which depends of the module 'account', add the following python code in it, and install the module.

I let you to create signed fields corresponding to fields I created (note I don't test this code, but should work)

from odoo import api, fields, models


class AccountInvoice(models.Model):
    _inherit = "account.invoice"

    @api.one
    @api.depends('invoice_line_ids.price_subtotal', 'tax_line_ids.amount', 'tax_line_ids.amount_rounding',
                 'currency_id', 'company_id', 'date_invoice', 'type')
    def _compute_amount(self):
        super(AccountInvoice, self)._compute_amount()
        self.amount_total_no_discount = sum(self.invoice_line_ids.mapped('price_subtotal_no_discount'))
	
    amount_total_no_discount = fields.Monetary(string='Total without discount', store=True, readonly=True,
	                                       compute='_compute_amount')

											   
class AccountInvoiceLine(models.Model):
    _inherit = "account.invoice.line"	

    @api.one
    @api.depends('price_unit', 'discount', 'invoice_line_tax_ids', 'quantity', 'product_id', 'invoice_id.partner_id',
	         'invoice_id.currency_id', 'invoice_id.company_id','invoice_id.date_invoice', 'invoice_id.date')
    def _compute_price(self):
        super(AccountInvoiceLine, self)._compute_price()
	if self.invoice_line_tax_ids:
            taxes = self.invoice_line_tax_ids.compute_all(self.price_unit, self.invoice_id.currency_id, self.quantity,
			                                  product=self.product_id, partner=self.invoice_id.partner_id)
	    self.price_subtotal_no_discount = taxes['total_included']
        else:
	    self.price_subtotal_no_discount = self.price_unit * self.quantity
	
    price_subtotal_no_discount = fields.Monetary(string='Amount without discount', store=True, readonly=True,
	                                         compute='_compute_price')

Regards