I get this error when confirming the quote:
<class 'NameError'>: "name 'self' is not defined" while evaluating
"deliveries = self.env['stock.picking'].search([('sale_id', '=', self.id)])\nfor delivery in deliveries:\n delivery.action_cancel()"

I have updated the answer, remove the self and try.

Thanks for taking the time to help me, it didn't work either, now it shows me an error in self.id, I'll keep looking for more options..
Thank you!

please try this,
self.env['stock.picking'].search([('origin', '=', self.name)])

thanks!