The parent was complaining about being forced to use OS X. So, the "walled garden" is intended for the underlying hardware.
I don't think that is what he was saying at all.
Regardless.
There is nothing preventing Linux (or Windows) from booting on Mac M1 hardware. People almost certainly will have Linux running on Mac hardware before too long. It's just a slog getting it working well.
Not a walled garden in any traditional sense, just difficult to implement.
Linus has been lusting after Apple hardware for a long time. He's also been exceedingly frustrated by the lack of drivers for most of that time.
8 years ago in an interview with Tech Crunch, he waxes poetic about the MacBook Air:
> "That said, I’m have to admit being a bit baffled by how nobody else seems to have done what Apple did with the Macbook Air – even several years after the first release, the other notebook vendors continue to push those ugly and clunky things. Yes, there are vendors that have tried to emulate it, but usually pretty badly. I don’t think I’m unusual in preferring my laptop to be thin and light."
https://techcrunch.com/2012/04/19/an-interview-with-milleniu...
I don't see his criticism of Apple drivers in this article, but he was pretty frustrated even back then.
Except the iOS-like secure boot verification and complete lack of any kind of documentation or drivers for the hardware. Details!
The other policies available are a) verify at install time the boot kernel is signed by Apple and is the most currently available version (default) or b) to verify at install time the boot kernel is signed by Apple without doing an online check (allows downgrades).
In all cases it's the same underlying mechanism that records what the system should be allowed to boot (according to whatever policy is in effect) and verifies at boot time it hasn't been tampered with. Big Sur takes that further and cryptographically verifies the entire system volume hasn't been tampered with (even offline).
You are correct that Apple does not provide drivers for other operating systems for M1 Macs.
Which Apple has documented how to work around.
> ... or drivers for the hardware.
Which is why I said it was going to be difficult to implement.
> ... Details!
Were apparently ignored.