But the point is - there's no fundamental restriction from the OS itself.
Whether you want to call it a “restriction”, “a lack of permission without being X type of activity”, or “it works because the app exhibits Y behavior”, it’s all functionally a restriction.
You can run some background activities that are not audio apps, but you’re at the mercy of iOS’s decision to keep your task active or not. If you’re off the charger, all bets are off. iOS’s dev docs make this very clear.
You say that, but then you dedicate a whole paragraph to my potentially (I’m not a native speaker, so it’s very possible) incorrect word usage :)
But also, I took your advice and had a chat with an LLM – seems like it's pretty much in agreement with my understanding of the meaning of "fundamental" as a plausible one.