CNPG is quite nice and robust but I'd still be a bit reluctant to stack PG on k8s for really big clusters just because k8s ecosystem moves quite quickly and there's lots of patching/maintenance/churn which means more PG failovers so depends on how well your workload handles that (they're normally only a few seconds)
Most K8s upgrades can happen independently of node reboots etc., you only need to update for OS updates really, but that would be true of anywhere you run PG, even RDS.
loading story #48492622