To implement a "Pay after Delivery" option without extensive customization, duplicate the existing "Wire Transfer" payment method and rename to something like "Pay after Delivery." Modify the instructions or success message associated with this new payment method to clearly inform customers that they should only initiate the wire transfer after receiving their order.
Additionally, update your order confirmation email template to reinforce these instructions, providing the necessary payment details and any other relevant information about the "Pay after Delivery" process. This approach focuses on clear communication to manage customer expectations without altering the fundamental checkout flow.
https://www.odoo.com/documentation/18.0/applications/finance/payment_providers/wire_transfer.html
If you need custom solution then look for some Odoo developer and they will update the checkout workflow.
I hope it helps!
Thanks,
Abhay
https://apps.odoo.com/apps/modules/18.0/website_pay_later