We're currently running v1.26.13 which has dropped off the list of supported versions.
$ doctl kubernetes options versions --context releng Slug Kubernetes Version Supported Features 1.29.1-do.0 1.29.1 cluster-autoscaler, docr-integration, ha-control-plane, token-authentication 1.28.6-do.0 1.28.6 cluster-autoscaler, docr-integration, ha-control-plane, token-authentication 1.27.10-do.0 1.27.10 cluster-autoscaler, docr-integration, ha-control-plane, token-authentication