I consider that "everything around it" (The Ecosystem, as they say) to be part of the product I bought. When I bought my OldPhone N years ago, I could go to the app store and download versions X, Y, and Z of apps A, B, and C, and they worked. I expect today that if I factory reset that OldPhone back to fresh, I'd still be able to re-download those compatible versions of those apps, and that those apps continued to work as they did N years ago (barring some obvious, but still unfortunate cases like companies going out of business or turning down online services). That's my bar for "working."
If the world moves on, and people are sharing image formats that my phone was never able to read in the first place, or writing web pages my browser was never able to render correctly, then I have to accept that. But what I don't accept is the device manufacturer, or (usually the case) 3rd party apps telling me "your phone is too old, and we're no longer going to let you use it as you have for the last N years anymore!"