It won't be an option for any current Inspiron systems.  You could locate a system from a retailer that had shipped with Windows 10, consider an outlet system with 10 -- or order a business (Latitude, Precision and some XPS models) that do offer an option for Windows 10. You can't configure anything other than what you see on the order page -- and just about all the current consumer systems (Inspirons) have Windows 11 only now.  
Hello, I would like to order a Dell Inspiron 15 laptop with Windows 10 vs. Windows 11.  I do not see this option for any Inspiron laptops on the website.  Is this option still available?  Do I need to contact the Sales department over the phone to purchase a laptop with this configuration?  
Dell Inspiron 15 with Windows 10