You may be talking about 2 different things:

1. Yes, ChromeOS is based on Linux, but it's not really what most people would refer to as "Linux". I think this is what you're talking about.

2. ChromeOS does have, however, some great technology to run an unrestricted version of Linux in a container, called Crostini: https://chromeos.dev/en/linux . I used to use a high end Pixel book (which was a great machine, really sad Google discontinued it - surprise, surprise, I know) as a primary dev laptop, it ran VSCode, postgres, etc. very well.

Yes, it is based on Linux, as are many televisions, car radios, phones, and other devices. That's my point re "smart" devices.

Crostini is a VM, and isn't 100% unrestricted. I'd classify it in the same category as WSL or Parallels.

Describe a way in which the Linux implementation of ChromeOS is “restricted”.

Disclaimer: I daily utilize a cheap Chromebook as a lightweight typewriter, and I love it.

However, it's important to note that Linux on this device is subject to certain restrictions: It operates within a containerized environment, which limits both disk space allocation and system-wide access. Accessing the terminal requires navigating through a "virtual machine", and files are shared within the /mnt/chromeos directory. Additionally, the utilization of USB devices is layered behind the primary operating system support and Linux backups are separate from the overall operating system backups.

Something interesting about Crostini is that it uses 9p to bridge filesystems, just like WSL2. It seems that 9p has "cracked the code" on bridging filesystems over virtual machines and differing operating systems in a way that other options never seemed to do quite as seamlessly, which I find rather interesting. Maybe it's because it comes with less baggage than CIFS? Easier to extend? Less complex than NFSv4? I'd love some commentary on this.

The filesystem bridging between Crostini, the rest of ChromeOS, and Google Drive is brilliant. It also transparently integrates SSHFS into the filesystem and the file browser.

Yes. You're describing Crostini which I use often and like. Those constraints are fine with me. YMMV.

If you want uncontainerized Linux you have to dual-boot. I used to do that but it's difficult and no longer worth the hassle IMO.

Well, for starters, with dm-verity and secure boot to prevent modifications to the root filesystem.

IMO it's beside the point. Calling ChromeOS "Linux" is like calling cells "mitochondria". One could argue that the same could be said about the somewhat standard Linux desktop stack you'd find on Ubuntu or Fedora installs, and that's true. However, that's probably mostly just a consequence of the fact that Linux doesn't have an actual standard userspace. The closest it has is the defacto set of components you're likely to find in any GNU/Linux distro, and they are quite different than what you'll find when you boot up ChromeOS or Android.

Are we talking "Linux, the kernel", or "Linux, the typical user experience"?

I reject the idea that a terrible UX is an integral part of Linux.

Inability to change DE, upgrade kernel, use kernel modules, etc.

Kernel changes that are not in the upstream kernel yet for one

Is spyware.

You can switch any chromebook into "developer mode". Then you get bash within the terminal app, with full sudo access.

At that point, as you poke around, you find that chrome os is actually built on top of gentoo Linux.

And there is a 3rd party pkg manager (chromebrew) which gives you gcc, and thus a whole host of additional pkgs.

Yup, its linux all right. Even without going the crouton (chrome into another distro) or crossing (vm running separate linux distro) route.