There are some native Magento features that you might consider using before engaging in customization.
Firstly, Magento supports bundled products. This allows you to create a bundle where the shopper has to get multiple items. You can make items required, and you can also give shoppers options to choose between. So, perhaps you'd have a cell phone screen repair service as a fixed item (no choices) + a cell phone screen with a dropdown of options. https://docs.magento.com/user-guide/catalog/product-create-bundle.html
Another solution could be using Customizable Options. This allows you to add an option to the product page. This option can be Required so that the shopper has to have it in order to make the purchase. It can have a price, etc. https://docs.magento.com/user-guide/catalog/settings-advanced-custom-options.html
Perhaps, between these two options, you wouldn't need an extension. Depending on your needs, you could try to apply a bit of customization without needing an extension. For instance, with the Customizable Option, you could do a bit of coding to hide it from the product display page. That would allow the required [additional] product to show up in the cart after the shopper adds the main item from the product display page to the cart.
Best of luck!
