I sell original artwork and offer upsells like mounting paper paintings and adding frames to canvas.
If the there is only the art variant for the product that leaves 2 options: paper and frames.
If your upselling as seperate products you just need to present those upells on the product page
Or in the cart like with the gift wrapping tutorial https://help.shopify.com/en/manual/online-store/themes/os/customize/add-gift-wrap-option
There’s also presenting such things as an order form
https://community.shopify.com/c/shopify-design/forms-add-an-order-form-to-your-store/td-p/613671
The reality is most merchants do not need interconnecting systems like this built into products forcing other products, there are enough apps and api features that specific merchant needs can be built by those merchants.
Until shopify decides to change this for just invest in the proper tools, there are many customization services available and numerous apps for product personalization, upsells, etc