The difference is that Apple's online features actually work, and are genuinely pretty good
The other thing is that iCloud offers Advanced Data Protection as an option, which completely E2E encrypts your cloud backups in such a way that even Apple can't access (and also comes with a disclaimer warning the user that their data will be inaccessible if they ever lose the backup keys).
They're one of the few big tech companies that routinely tells the US government to pound sand when they come knocking without a warrant (and even sometimes when they do).
I'm not sure. Macs usually only get OS support for ~7-9 years, but I don't think they've ever disabled activation services for older devices.
The update servers for the old PowerPC Macs are still running. If you can get an iBook G4 on the internet, you can still download updates.
My understanding (happy to be corrected by the more Mac-literate) is that part of the initial setup is calling home to Apple servers to generate an owner key that's used to grant your newly created admin account rights to modify key boot and settings
You do need a connection during first setup to activate (as far as I know anyway, I've never setup a completely new Mac without internet), but afterwards the secure enclave on the M-series chips has all the functionality necessary to reprovision the machine in the event of a complete wipe. You will need to bring a second mac so you can use DFU, but the entire process can be done entirely offline as long as you have a second mac (or something sophisticated enough to pretend to be one for DFU purposes).
But in any case - the way MacOS on Apple Silicon works is a bit different. The core OS is kept in an immutable section of SSD that only signed MacOS updates can alter. Even if you want to boot Linux or something, you boot into a stripped-down MacOS first which then transfers control over to Linux. Very hard to fuck up a modern MacOS install in a way that's permanent because the essential parts of the OS are always out of reach of most software (which is also why Apple has nerfed KEXTs so much on Apple SIlicon).
Also, what about running software that doesn't come from the online store "sideloading"?
All software on MacOS must be signed (this is to prevent malicious tampering with executables after approval). You don't need a signature from Apple and a lot of app devs just self-sign (anything built for MacOS using the standard toolchains will be self-signed by default). The only downside to self-signing is that there's additional dialogue boxes for the end-user to jump through to run your software.
Most software is obtained from outside the app store and there's actually good reasons why. App Store enforces a kind of strict sandboxing on applications that can degrade functionality (good example is Scrivener, which doesn't support a bunch of external document formatting scripts when you buy the app store version).
You don't have to be online to get software though if that's what you're asking. If you have .app file for the software you want to install, then it's usually as simple as copying it into your Applications folder.
