Preventing Reserved Units selection starting from CRM Opportunity (No-Code approach)

ERPNext Selling/CRM
1

Hi everyone,
I’m a Junior Implementer working on a Real Estate project. I’ve seen the new Stock Reservation feature in ERPNext, but it seems to trigger the validation at the Sales Order stage.
In our business case, we need to prevent Sales users from selecting a unit starting from the Opportunity or Quotation stage if that unit is already reserved.
My Constraints:

  1. I want to achieve this using Standard/No-code configuration.
2

only way i see is clientscripts

3

Thank you