CONNECT denied (ask the admin to allow HTTPS tunnels) when running docker pull hello-world

Hello,

setting up docker on Ubuntu 18.04 LTS along https://docs.docker.com/install/linux/docker-ce/ubuntu/ works, the daemon is running.

But the simple docker pull hello-word runs into error:

docker pull hello-world Using default tag: latest Error response from daemon: Get https://registry-1.docker.io/v2/: CONNECT denied (ask the admin to allow HTTPS tunnels)

Corporate proxy is enabled like this:
systemctl show --property=Environment docker Environment=HTTP_PROXY=http://Corp-IP-Addr:proxy-Port NO_PROXY=localhost,127.0.0.1,::1
IP and port obfuscated.

Any help appreciated, thanks.