I agree, this is 90% likely malicious. The non-malicious usage I can imagine is that for debugging the firewall you don't want to lock your other services out of it in case something goes wrong (or as you said, for reliability issues)
> It’s worth noting that Big Sur and its predecessors are built to assume that they can talk to Apple at any time, but when we don’t allow it, a few unwanted side effects pop up. For example, the keyboard sometimes takes longer to wake up from sleep mode. Or, in certain situations, the Mullvad app takes longer to detect that the computer is online.
- https://mullvad.net/en/blog/2020/11/16/big-no-big-sur-mullva...
(Ofcourse, as a developer, I can sympathize with the Apple developers - when you design a product to use the internet, you don't really think hard about all kinds of use cases where internet access is deliberately denied).
Why wouldn't you, though? That seems like a pretty big oversight. Lazy at best, negligent at worst. Not everyone in the world has constant internet access, and it seems ridiculous to design an _operating system_ with that assumption. I like to take an eBook reader to the park, for example. Prior to owning that device, I took a laptop when learning a new programming language. If that laptop had been running BigSur, I'd see all these same issues based on Apple's un-thought-out "design decisions".