[SirMittens]

Afaik,

- Xbox is basically using Windows Core + the xbox shell and runs the games in virtual machines.

- The PS4/5 use FreeBSD with their shell and libraries on top.

- The Steam Desk ships Linux and a shell on top of it (Steam Big Picture + Proton).

modern consoles are just PCs using PC OSs with custom UIs that fit the control scheme.

The only one that I could think of that's heavily modified is the Switch.

[flohofwoe]

I only know the dev environment on the Xbox up to 360 and the Playstation up to PS3, but both have OS APIs that differ quite a bit from their 'desktop counterparts'. E.g. even though the PS has a FreeBSD kernel, this has little relevance for development on the console, it's just a shortcut for Sony, but not for game devs (for instance the 3D rendering, sound, input etc... APIs are completely custom). On the Xbox it was the other way around the kernel was written from scratch (AFAIK) but had some stripped down Win32 and DirectX APIs layered on top to simplify porting, but in any case the system APIs were different enough that one couldn't simply move much existing code based over without at least some adjustments. Some game dev APIs originating on the Xbox were even moved to Windows, to simplify porting Xbox games back to Windows.

[SirMittens]

That is very true for the the consoles before the Xbox One and PS4.

However, since the release of those 2, seems like Microsoft and Sony use an off the shelf OS + their Shell and APIs (graphics, networking, matchmaking ...etc), which makes sense, especially for Microsoft, as they already develop a very capable x86 kernel, so why not use it.

Afaik, with the introduction of the Xbox one, they used the Windows 8 Core as part of their "One OS" strategy to unify all of their devices on the same platform/OS (eg. consoles, mobile, AR/RV, PCs ...etc).

The current version of the Xbox OS is based on Windows 11 [0].

Ofc, it's not exactly the same as Windows, but, it's largely based on it, at least as far as we know.

[0]: https://en.wikipedia.org/wiki/Xbox_system_software

EDIT: Added the wikipedia link. It's the only source I could access from my work's network, but it show's the OS progression since the the first generation Xbox