Deleting all instances of resource type across multiple/all Kubernetes namespaces

Solution 1:

You should delete the whole crd (Custom Resource Definition), first list your CRDs with

kubectl get crd

and then delete the CRD, with e.g. (using Issuer as example)

kubectl delete crd issuer.<something>.<something>

When the CRD is deleted, also all instances of that CRD (e.g. all resources of kind: Issuer) is deleted.