odoo-product-addons/product_variant_description_sale/models/product_product.py

from odoo import models, fields


class ProductProduct(models.Model):
    _inherit = "product.product"

    variant_description_sale = fields.Text(
        "Variant sales description",
        translate=True,
        help="This note is added to sales orders and invoices for this particular variant.",
    )

    def get_product_multiline_description_sale(self):
        name = super().get_product_multiline_description_sale()
        if self.variant_description_sale:
            name += "\n" + self.variant_description_sale
        return name