> In case of an app, what is the "product" you are buying?

The app.

> Because according to Apple, they add a lot of "value" by ensuring the software is safe, performant, etc etc. Am I not buying "a safe, checked app"? Or am I buying an app and then separately pay Apple for an added service of "checking the app for safety" etc etc. I'd very much presume the first.

If you want to, you can imagine the 30% cut being that separate service, but most analyses I've seen of this assume the first is the case, and I can't really see why it wouldn't be.

> But many apps are really a service or even more that happen to have "an app" as one of the ways to interact with the service: Netflix, Uber, protonmail, Vinted (or ebay), etc etc: the app isn't the thing I buy.

In those cases the app on the App Store is free, so there's nothing a consumer can really complain about, since they haven't bought anything. You can complain about the service rendered when you pay, but that purchase is handled completely separately from the app (non-)purchase.

> Point being: It's not simple, so your answers don't fit the analogy of "wallmart".

It does for apps bought as products. If you want an analogy for apps bought as services, then I'll use a different analogy, since they behave differently, and are treated differently in law.