From Android Nougat you can display two activities side by side in same app using FLAG_ACTIVITY_LAUNCH_ADJACENT when launching a new activity.
As per doc
When you launch a new activity, you can hint to the system that the
new activity should be displayed adjacent to the current one, if
possible. To do this, use the intent flag
FLAG_ACTIVITY_LAUNCH_ADJACENT. Passing this flag requests the
following behavior:
If the device is in split-screen mode, the system attempts to create
the new activity next to the activity that launched it, so the two
activities share the screen. The system is not guaranteed to be able
to do this, but it makes the activities adjacent if possible. If the
device is not in split-screen mode, this flag has no effect.