I think you’re running into this problem which is due to zero-to-jupyterhub overriding the default Docker command.
You can restore the default in Z2JH by setting singleuser.cmd to null:
singleuser:
cmd:
That’s a PR discussing whether we should remove the override in Z2JH to avoid these sorts of problems: https://github.com/jupyterhub/zero-to-jupyterhub-k8s/pull/2138
but