Sure. Whatever. Go back and read the first post you replied to. I was specifically explaining to someone why using iOS on the outside display and iPadOS on the inside display is not simple without reworking.
Look, they're *the same OS*. They have some different APIs exposed, but they're exactly the same under the hood. MacOS, iOS, tvOS, iPadOS, watchOS, etc are all the same OS.
They're all Darwin/XNU (aka the current version of NextSTEP pretty much) with mostly the same tooling, drivers, and even mostly the same APIs.
There's some differences in APIs exposed, slightly different bootloader config on MacOS, and some differences in what is allowed in userland depending on the device (but, for example, if you jailbreak an iOS machine and drop into a shell you'll be in an environment pretty much identical to macOS, up to an including all the GNU applications, and the ability to run binaries or even install a whole build toolchain).
The naming differences are more about focusing Apple's dev teams and marketing for consumers. Each is a logical seperation, not a different OS in the technical sense. Apple's core OS team is the same for everything.
Shifting what APIs are available based on devices plugged in and active (which is essentially how you handle multiple screens, no matter internal or external) is not hard, and is already done *all the time* on everything from assistive devices to attached auxiliary devices like watches and headphones to network adapters to GPUs, to etc.
Shifting windowing sizing and modes based on displays is already normal on all these devices.
Even, going into userland, services like a browser are built in in places you may not expect - a good example of that is something you can test right now is messaging yourself a link and then clicking it on an aWatch. Safari isnt an available app in the app list, but it's on the device and it will load the webpage. You can browse the web on your watch, albeit it's a pain (I usually use that capability to look up things on wikipedia or quick googles on my watch when I'm not near any other device)
And most popular iOS apps also already have iPad modes too (like, say, the NYT app). Apps that dont still run on iPads but stretched (like Instagram until very recently), they work just fine. MacOS has the full iOS and iPadOS API available too, the only reason not all iOS/iPadOS apps arent available on MacOS is Apple doing some gating with signing to give the developers the choice, that's why when they first enabled iOS apps on macOS you could use iMazing to download any of your apps and fire them up on your mac. They've improved their gating, but the capability isnt limited.
at *worst* Apple would have to run 2 different windowing managers (which is a *long* solved problem, I used to run multiple copies of X on Linux machines like 30 years ago), and there's no real reason for that, I gaurantee they'll either just allow apps to switch to iPad format when a folding device is open or create a new intermediate mode. Apps that dont support switching initially, probably ones that dont have iPad scaled options, will simply get stretched or letterboxed, just as now. Other than that it wont be any different from plugging an external monitor to your macbook and then closing the laptop, it just shifts everything to the only active display.
