I don't doubt the features are there, I'm genuinely curious what they are.
- All user data is encrypted at the login level. A guest user cannot access any other users’ data. Whereas in Ubuntu, for example, home directories have 755 permissions.
- The Linux userspace in ChromeOS is actually running on KVM, so ChromeOS itself is insulated from user-installed malware.
- Verified boot is huge. It is theoretically impossible for a modification to system-level software to survive a reboot. An attacker would have to modify the hardware too. And even if someone stole your Chromebook and modified the hardware to run malware, your data is still encrypted.
If you are interested, a more thorough explanation can be found here: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/sec...
Or, put another way: your threat model is a nefarious hacker or three-letter-agency who might secretly modify your hardware/software to get your data. Mine is surveillance capitalism. ChromeOS is secure under your threat model, but is _built by the attacker_ under mine.
Both of these threat models are important to consider, but one is much more relevant to a larger portion of the population than the other.