Thanks to @luk3202, i corrected.
But as well, i had to specify the launch-type="FARGATE", see also:
AWS ECS Error when running task: No Container Instances were found in your cluster
and also {"assignPublicIp": "ENABLED" ...
Thus in my example the solution is:
aws ecs run-task  --cluster tryimport --task-definition fromecr:2 --launch-type="FARGATE" --network-configuration '{ "awsvpcConfiguration": { "assignPublicIp":"ENABLED", "securityGroups": ["sg-e9bd4ab9"], "subnets": ["subnet-0b170efc0b8f6f53b"]}}'