How can I track user-selected product settings beyond default variations?

[RikutoNakamura]

I'd like to have detailed settings on the product detail screen, apart from the shopify default variations.
I'm trying to manage user-selected settings in the app's DB.
However, I don't think the script can be loaded in the checkout screen in the normal shopify.
In this case, how can I make a POST request for detailed settings for a product?
I want to keep track of which settings my purchased users have selected.