MacOS’s security is great but unfortunately not open source

QubesOS’s sandboxing/virtualization is way above whatever you can do on Debian

Both Kernel and userland

Android runs a linux kernel yes but is very far from normal linux distros, it almost alleviate all of problems with linux

Hurd kernel’s concept seems solid but it doesn’t look like actively developed?

OpenBSD might be best choice as you say at least until Genode or something similar become useable

As I mentioned in post Kicksecure plans to harden Linux but is not there yet, For virtualization and containerization there is QubesOS but still that doesn’t seem ideal and it requires some beefy hardware

More info on Atmosphere as I find it fascinating that an OS created for a gaming device got such tight security:

https://www.reddit.com/r/emulation/comments/hygtnx/mesosphere_opensource_nintendo_switch_kernel_now/

“It is a completely unique microkernel with a cooperative (non-preemptive) scheduler. The kernel is secure – so far as I can tell (as a reverse engineer and hacker), it has zero security bugs. They throw out years of backwards compatibility (they’re not POSIX/UNIX), and they really, really benefit from it from a security and modularity PoV. Horizon’s the only meaningful RTOS with a microkernel that I’m aware of (other than Fuschia). Everything’s in userland – filesystems, gpu (and other device drivers). The OS is capability-based and conceptually all about lots of different processes/drivers (“system modules”) that host microservices. The fact that Nintendo designed such a rock-solid, modular, custom operating system for their consoles fascinates me.”

“IPC is the hottest hot-path in a microkernel, correspondingly Nintendo marked every function involved in IPC as attribute((always_inline)), this was kind of a huge pain to reverse engineer as a result. In addition, Nintendo implemented “SvcReplyAndReceive” as a single system call that allows a microservice server process to reply to and receive a new message in one invocation. That said, there’s actually less overhead than you think. Past of why FUSE is slower than a kernel driver for FS is because FUSE has to talk to the kernel to do filesystem stuff, so when you read a file you have your process -> FUSE -> kernel -> hardware. In comparison, on Horizon the kernel is completely uninvolved in filesystem management (it doesn’t even have the sdmmc hardware mapped). Thus processes will do process -> FS system module process -> hardware.”

“In Horizon, everything is very distinctly not a file. There’s no global filesystem paths the way that unix/linux have special /dev/whatever. Pipes don’t exist in Horizon – all IPC is done via the horizon ipc (“HIPC”) protocol. UNIX/POSIX have stuff like fork() and child processes…but creating a process is an incredibly privileged operation in a capability-based operating system. Fork() is impossible to implement in Horizon, all threads are created via SvcCreateThread() instead. Child processes aren’t a thing that exist.”