Sysbox kubernetes install fails behind HTTPS Proxy

When installing sysbox via kubernetes (in a Rancher 2.6 downstream cluster with k8s 1.21.10) behind a Internet HTTPs proxy following the instructions on https://github.com/nestybox/sysbox/blob/master/docs/user-guide/install-k8s.md using Ubuntu 20.04 (latest) as node OS all pods on the node(s) where sysbox should be installed report the following issue during "container creation" in Rancher 2.6:

Failed to create pod sandbox: rpc error: code = Unknown desc = error creating pod sandbox with name "k8s_cattle-node-agent-5mdcl_cattle-system_534ba7cd-b43f-4911-a1a6-4346e0d75d06_0": Error initializing source docker://k8s.gcr.io/pause:3.5: error pinging docker registry k8s.gcr.io: Get "https://k8s.gcr.io/v2/": dial tcp: lookup k8s.gcr.io on 127.0.0.53:53: server misbehaving
Failed to create pod sandbox: rpc error: code = Unknown desc = error creating pod sandbox with name "k8s_coredns-685d6d555d-wbm64_kube-system_8b8b549e-52e1-44ff-b825-f7c6eee340a4_0": Error initializing source docker://k8s.gcr.io/pause:3.5: error pinging docker registry k8s.gcr.io: Get "https://k8s.gcr.io/v2/": dial tcp: lookup k8s.gcr.io on 127.0.0.53:53: server misbehaving

Is there a workaround to specify proxy information (HTTP_PROXY, HTTPS_PROXY, NO_PROXY) to the installer (install.yml) or is this setup not supported at all if located behind an Internet proxy?

(Searched the Web but did not find a single hint so far)