But the nice parts of ChromeOS, as far as security properties go are the way it can be "power washed" between usages. Along with a desktop Linux system that has less binaries installed at it's base than most. And things that are built in are typically built atop chrome's sandbox.
I used to joke with my friends who ran TAILS Linux that my grandma with her Chromebook had the same threat model.
OpenBSD's track record is impressive but is it a significant target compared to Windows, MacOS, and Linux?
It is easy to say "only two bullets have ever penetrated my armor" when hardly anyone is shooting at you. I do not know if this is the case because I have never used OpenBSD and I do not know how widely it is used (headless servers, embedded devices, etc.).
You can read more about OBSD's security by going to https://openbsd.org then clicking the "Security" link near the top left.
ps: FreeBSD seems to have more users than OpenBSD, and NetBSD seems to have fewer users than OpenBSD.
Also I separate things by user account, so I don't do my general browsing as the same user that does my programming, which is again separate from bank access, which is separate from .... So the kernel is providing a lot of protections.
(And I usually browse without images and javascript, which is not OS-specific but a suggestion. Many things I use don't require it, and I can flip it on or configure it specifically for those that do.)
Do jails not fulfill this?
I talked to a security researcher specializing on Android at a conference and he didn't sound like he'd agree.
While I personally think ChromiumOS does a good job, I think a huge problem is that the issue is in how liberally complexity is added. And complexity is typically where security issues lurk. This has been seen again and again.
It's also why I think projects such as OpenBSD do such a great job. Their main focus seems to be reducing complexity (which they are sometimes are criticized for). A lot of the security seems to come from the reduced attack surface you get. And then the security mechanisms build, which typically are more easily implemented, because of said simplicity are the next layer.
And I think OpenBSD has reached a sweet spot there, where it's not some obscure research OS, but an OS that you can install on your server or desktop, run actual work loads, heck, even play Stardew Valley, or a shooter on, but have all the benefits in terms of security or simplicity that you can from research OSs, Plan 9, etc.
So maybe not mainstream, but mainstream enough to actually work with it. There's sadly many projects that completely ignore reality around them, also because their goal is to simply be research projects and nothing more. Then we have those papers that rarely everyone ever looks at on how in a perfect world all those big security topics could be solved. Unless some big company comes along and puts it into some milestone.
ChromiumOS seems like the limitations you get are similar, probably even more severe than what you get compared to OpenBSD's flexibility. That's something many de-google projects struggle with as well. At the same time the complexity remains a whole lot bigger. Of course goals and target groups are hugely different.
I think both Android and ChromiumOS used to put more emphasis on simplicity, but gave it up at some point. I am not sure why, but would assume that many decisions are simply company decisions. After all the eventual goal is economic growth.
That locking down on mobile devices is not just to increase security, but has the beneficial side effect of controlling the platform. This might not even be directly intended by the security focused developers, but it is a side effect.
So "most trustable" in that scenario comes with "most gate-keeping", "least ownership", etc., which we are kind of used to on smartphones, tablets and Chromebooks. So I think comparing it with other kinds of mainstream OSs isn't really leading to much.