Hi,

Try to refer the following code.

from odoo import models, api, exceptions

class SaleOrder(models.Model):

    _inherit = 'sale.order'

    def action_confirm(self):

        for line in self.order_line:

            product_qty_available = line.product_id.qty_available

            if product_qty_available < line.product_uom_qty:

                raise exceptions.Warning('Not enough stock available for product %s. Available quantity: %s' % (line.product_id.name, product_qty_available))

        return super(SaleOrder, self).action_confirm()

Hope it helps