In this case, if you are using default LocalProcessSpawner, the single user server logs will be logged to the same JupyterHub logs. As you are using systemd to manage JupyterHub, the logs will be available via journalctl I imagine?
If you could share your config and logs that shows events from user logging in to spawning a server, we could try to find where the issue lies for you.
I think it was because we are running Jupyterhub with Lab on version 4.0.1 that due to some lower environment requirements we are unable to install correctly due the requirement of nodejs 18 which in turn requires a version of glibc available only on RHEL8.