Comment 3 for bug 1974082

> I have the same issue also, it seems that with yoga/stable channel of nova-compute charm the nova.conf is rendered using /var/lib/juju/agents/unit-nova-compute-6/charm/templates/train/nova.conf template which is old and has no [vnc] section.

Yes, this is an issue. More interestingly, it's due to the (deprecated) vncserver_proxy_address being removed at yoga and only using the server_proxy_address: https://docs.openstack.org/releasenotes/nova/yoga.html#upgrade-notes

For future travellers: move the vnc options into a [vnc] section in a newly created ./templates/yoga/nova.conf.

Fix on master, then backport to stable/yoga branch.