I think some manufacturers offer the ability to buy hardware without software preinstalled and have the software as add-ons you can opt-in. That should be the way.
I applaud Dell for offering this as an option, and for getting Ubuntu certification even on many devices which don't offer it. However, in practice it's not worth much because the standard configurations are discounted, while custom configurations with Ubuntu are not. For example, in this configuration Ubuntu is listed as $140 more than Windows. If you click the info icon, it's because it's $60 cheaper but loses you a $200 discount: https://www.dell.com/en-us/shop/dell-laptops/new-xps-14-lapt...
I think they should note that on the page, because it makes it look like Dell is a bad vendor but in practice they're one of the better ones, in this aspect.