This is a paid asset, but now you can download Dynamic Split Screen Free.
Detail this asset from Unity Store: Original Link
Dynamic Split Screen v1.1 (Latest version)
Dynamic Split Screen provides a quick way to prototype 2 player split screen project without caring about rendering.
Supported modes are 2D and 3D top-down view (with camera looking from an angle).
Cameras positions are updated dynamically based on relative player positions, if they are close enough, they will be rendered on single screen.
– 2D and 3D top-down view support
– custom split line support
– dynamic split screen rotation
– support for changing player screen size and split angle
– ability to change camera distance / ortho size
And all of this works with minimal effort, custom setup takes just 2 clicks and 1 line of code. Sample scenes and documentation are available as part of the package too.