Install Operator on OKD - "no kind "AdmissionReview" is registered for version "admission.k8s.io/v1"

Hello there,

I have an OKD 4.8 cluster and want to install/configure the current runner operator (1.6.1) as described in https://docs.gitlab.com/runner/install/openshift.html

Everything works fine until creating the CRD (last step). When applying gitlab-runner.yml, the manager throws an error:

ERROR	controller-runtime.webhook.webhooks	unable to decode the request	{"webhook": "/validate-apps-gitlab-com-v1beta2-runner", "error": "no kind \"AdmissionReview\" is registered for version \"admission.k8s.io/v1\" in scheme \"pkg/runtime/scheme.go:101\""}
github.com/go-logr/zapr.(*zapLogger).Error
	/go/pkg/mod/github.com/go-logr/zapr@v0.1.0/zapr.go:128
sigs.k8s.io/controller-runtime/pkg/webhook/admission.(*Webhook).ServeHTTP
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.6.3/pkg/webhook/admission/http.go:79

and the runner is not registered, obviously.

Can you give me a hint?

Kind regards,
Hauke