When all FlutterEngines from a FlutterEngineGroup are destroyed, the next
FlutterEngine created has the same performance characteristics as the very
first engine.

The FlutterEngineGroup itself doesn’t need to live beyond all of the spawned
engines. Destroying the FlutterEngineGroup doesn’t affect existing spawned
FlutterEngines but does remove the ability to spawn additional
FlutterEngines that share resources with existing spawned engines.

Communication

Communication between Flutter instances is handled using platform channels
(or Pigeon) through the host platform. To see our roadmap on communication,
or other planned work on enhancing multiple Flutter instances, see 
Issue 72009.

Samples

You can find a sample demonstrating how to use FlutterEngineGroup
on both Android and iOS on GitHub.