On BlueStacks, go to Settings and select the Engine tab and take note of your graphics mode settings.
XSplit Broadcaster works on both DirectX and OpenGL graphics modes. For laptop users, however, selecting DirectX may give better performance..
On XSplit Broadcaster: Go to Sources > Game Capture, then select BlueStacks (DX11) or BlueStacks (OpenGL) depending on the engine settings you have chosen on BlueStacks 3.
Selecting BlueStacks (DX9Ex) captures the BlueStacks 4 launcher instead of the gameplay.
Launch a game app on BlueStacks 4 and this should automatically appear on your Broadcaster's scene. You can start recording or streaming!