Yes, you can have privilege-based security without user accounts, if you accept that you do not have control over your own hardware because only the OS vendor has administrative rights.
In other words: yes, you can have no-sign-in and no user accounts, but it's still there and you don't have admin access to your own computer.
Stepping back a level:
Smartphone OSes do not show accounts and permissions, but they are still there, just concealed. Same as they still have complex filesystems, but they are hidden.
Stepping back another level:
This is a bad way to design OSes: when you need to hide away major parts of the functionality, then you shouldn't have that functionality. It should not be in your design in the first place.
> Yes, you can have privilege-based security without user accounts, if you accept that you do not have control over your own hardware because only the OS vendor has administrative rights.
Or maybe just that the really in-depth administration and modification of your operating system happens prior to the OS running on your device, when it's being built — as a sort of configuration or specification step that happens prior to even installing the operating system or booting up your computer in the the first place, in a continuous integration system in the cloud perhaps, or on another existing computer? That's kind of how Fedora Silverblue works — almost everything you do is completely in unprivileged space, in a container or with a flatpak sandbox, or through policykit; you basically never use the root account at all, because you can't really do a whole lot of really in-depth customization of your OS internals on the operating system image that's actually installed and running on your system. Instead, you specify the modifications you want to make to an upstream image using something like BlueBuild[1] and then those modifications are automated and happen prior to anything ever hitting your computer in an automated ci/cd system (which could theoretically be self-hosted).
Like, I think there is a way to adapt the security and reliability benefits of the way e.g. macOS works that doesn't take control away from the user, just moves it somewhere else. And I think it's much safer for all of the really deep modification of your system, all of the system administration you do as the root user, to be essentially air gapped from the computer that you're actually running various applications and installing and building things and curling to bash on, on a system that's ostensibly clean.
