Downloadable products refer to items that can be downloaded, such as eBooks, software applications, music, updates, games, etc. These products are digital and do not involve a shipping method at checkout after making a payment the products can be downloaded from the link or a file so there is no reason to enable COD for that.
First, add the entry for the new library in the package.json. Then, create a plugin for that library inside the JS file in the assets folder and load it in app.js. After everything is done, easily use it in the blade.
Currently, this functionality is not available by default. By default, a dropdown is shown on the product detail page where you can select the color as per your choice under a single parent product.
Kindly refer to the image in the link below for clarification: