I think two resized windows next to each other is all you're going to get if you want to automate it. There is no programmatic way to turn Split View on/off AFAIK.
Is it even possible to put another app on the same desktop as a fullscreen one?
It is. There are a couple ways that I know of.
The first one depends on our settings. If I have a full-screen app going I can go find the other app I want on that screen, click its top window handle and hold, then command-uparrow to see my desktops. Then I just drag it to the window and it will split the screen between them.
The other way is to click and hold the full screen button on the app's window bar. This lets you pick a side to put it on, then click any other app on that desktop and it will split between them.
In either case, you can drag the bar between the windows to divvy up how much screen each gets. And you can only do this with two windows.
As to doing it programmatically, I've never tried that and I suspect you can't. But it is possible otherwise.
Open an app directly in splitview
in Workflow Help & Questions
Posted
It is. There are a couple ways that I know of.
The first one depends on our settings. If I have a full-screen app going I can go find the other app I want on that screen, click its top window handle and hold, then command-uparrow to see my desktops. Then I just drag it to the window and it will split the screen between them.
The other way is to click and hold the full screen button on the app's window bar. This lets you pick a side to put it on, then click any other app on that desktop and it will split between them.
In either case, you can drag the bar between the windows to divvy up how much screen each gets. And you can only do this with two windows.
As to doing it programmatically, I've never tried that and I suspect you can't. But it is possible otherwise.