The whole definition is one of process, not of product. While it correlates with the nature of the end product it does not define the end product. Exactly the same end result with some steps done at home somehow magically changes the result.

And until we control for the proxy it's meaningless anyway. UPFs have a big problem in that people tend to consume too much (the expected endpoint of companies engineering for what people buy) and that causes a whole host of health problems. I haven't seen anything meaningful that differentiates UPF from overconsumption.