For stack_set_instance sequential deployment

hello,
it appears that aws_cloudformation_stack_set_instance can only deploy sequentially. Am i doing something wrong?

Code:

resource "aws_cloudformation_stack_set" "config_role" {
  lifecycle {
    ignore_changes = [administration_role_arn]
  }
  name        = "ConfigRemediationRole"
  auto_deployment {
    enabled = true
  }
  permission_model = "SERVICE_MANAGED"
  managed_execution {
    active = true
  }
  capabilities  = ["CAPABILITY_NAMED_IAM"]
  template_body = <<EOF
<yaml template>
EOF
}

data "aws_organizations_organization" "org" {}

resource "aws_cloudformation_stack_set_instance" "config_role_deploy" {
  stack_set_name = aws_cloudformation_stack_set.config_role.name
  deployment_targets {
    organizational_unit_ids = [data.aws_organizations_organization.org.roots[0].id]
  }
  region = var.region
  operation_preferences {
    max_concurrent_count = 4
  }
}

When triggered, the update is always sequential one at a time.
My expectation that an update to template will be deployed with up to 4 processes.