is there a way so set all gameobjects in the scene to passive, as long as they are not seen by the main-camera to save processing power? thanks!
You could use the event OnBecameInvisible to disable some time consuming jobs, and OnBecameVisible to re-enable them. These events occur when the object isn’t/is visible in any camera (including the scene view camera!). Animations use something like this when the cullingType is BasedOnRenderers (default) in order to save CPU time when the object isn’t visible.
Use this wisely: deactivating/activating the entire object based on its visibility may be more expensive than letting it alive all the time - it would be better to just deactivate slow routines or scripts.