Hi, is there a way to prevent that an Action Engine Signal is resolved by the system automatically, but can only resolved manually by the responsible user?

Yes this is possible

By the action engine skill, by actions you have two options: Actions and automatic actions. Automatic actions means that by actions, the execute for new signals is checked. Then the action will automatically and immediately be executed for new signals as the description states. When the action should be automatic, you can change the status after the execution for success and for error. For success, you can put 'awaiting confirmation' for example, which should mean it is waiting for confirmation from the user. You can check the other statuses, and select the best one which suits