I suggest that there is a variant of StartActivity that sets FLAG_ACTIVITY_LAUNCH_ADJACENT in the starting intent so that an Activity can be displayed alongside the calling Activity in split screen or multi-window mode. Having Activity.isInMultiWindowMode() available would also be useful.
There are most probably further negative ramifications in being able to do this which I cannot currently explore.
Sub Activity_Click
Dim in As Intent = GetActivityIntent(Activity2)
'add flags here
StartActivity(in)
End Sub
Sub GetActivityIntent (act As Object) As Intent
Dim ctxt As JavaObject
ctxt.InitializeContext
Dim in As JavaObject
in.InitializeNewInstance("android.content.Intent", Array(ctxt, act))
Return in
End Sub