The large advertising platforms have free, built-in tools that you can use to create dynamic ads or shopping campaigns. E.g. Facebook Ads or Google Ads. But these tools are limited:
❌ Limited functionality would not allow you to create an awesome design. The banner's customization is very minimal here.
❌ There is no image pre-processing. You can't change the contrast or brightness, there's no smart resize, etc. Images in Product Catalog have too much of an extra background space and you can't crop it.
❌ You would not be able to export several different elements (products) simultaneously from your Product Feed.
❌ You can't download the result (i.e. creatives) on your computer in case you would also want to use them on other advertising platforms.
If you don't want to have all these restrictions, then you should use an external Creative Ad Builder
for your Ecommerce Banners.