Your Kubernetes is too recent, as support for "apps/v1beta2" was removed in Kubernetes 1.16.
You can do either of the following:
Upgrade to DSS 8.0.1 which adds support for more recent Kubernetes
Downgrade to Kubernetes 1.15
Go to the DSS installation directory and edit the resources/api-deployer/kubernetes/deployment.yaml.template file. In the first line, replace apps/v1beta2 by apps/v1