Amazon Redshift should have automatic upgrades to major versions enabled

How to fix it

Set AllowVersionUpgrade to true on the cluster, so Redshift applies engine releases and the security fixes in them during the maintenance window. The flag takes effect at once, but the upgrade it permits interrupts the cluster when it later runs, so set the preferred maintenance window to a quiet period first.

In the console

Redshift → Clusters → the cluster → Maintenance → Edit → Allow version upgrade

With the AWS CLI

aws redshift modify-cluster --cluster-identifier <cluster-id> --allow-version-upgrade --region <region>

With Terraform

resource "aws_redshift_cluster" "this" {
  cluster_identifier    = var.cluster_identifier
  node_type             = var.node_type
  allow_version_upgrade = true
}