Currently `ECSOperator` propagates `platform_version` parameter either in case `launch_type` is `FARGATE` or there is `capacity_provider_strategy` parameter provided. The case with `capacity_provider_strategy` is wrong. Capacity provider strategy can contain a reference on EC2 capacity provider. If it's an EC2 capacity provider, then `platform_version` should not be propagated to the `boto3` api call. And it's not possible to do so with the current logic of `ECSOperator` because `platform_version` is always propagated in such case and `boto3` doesn't accept `platform_version` as `None`. So in order to fix that `platform_version` should be an independent parameter and propagated only when it's specified, regardless which `launch_type` or `capacity_provider_strategy` is specified. That should also simplify the logic of `ECSOperator`.

I will prepare a PR to fix that.
airflow/providers/amazon/aws/operators/ecs.py
"""
    Execute a task on AWS ECS (Elastic Container Service)
    .. seealso::
        For more information on how to use this operator, take a look at the guide:
        :ref:`howto/operator:ECSOperator`
    :param task_definition: the task definition name on Elastic Container Service
    :type task_definition: str
    :param cluster: the cluster name on Elastic Container Service
    :type cluster: str
    :param overrides: the same parameter that boto3 will receive (templated):
        https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ecs.html#ECS.Client.run_task
    :type overrides: dict