Hi,

You can define a compute field inheriting the res.partner model with the following function,

class ResPartner(models.Model):
    _inherit = 'res.partner'

partner_order_total_amount = fields.Float(
    string='Total Uninvoiced Sales Orders',
    compute='_compute_order_total',
    store=True
)

@api.depends('sale_order_ids.amount_total', 'sale_order_ids.invoice_status')
def _compute_order_total(self):
    for partner in self:
        total_amount = 0.0
        for order in partner.sale_order_ids:
            if order.invoice_status != 'invoiced' and order.state == 'sale':
                total_amount += order.amount_total
        partner.partner_order_total_amount = total_amount

Thanks