The only Runbook trigger right now is a scheduled trigger.

I would like to suggest two more trigger types:

Helm Chart Package Trigger:

When a new Helm Chart version of a package is published, then the trigger would fire. (Allowing the calling of a Runbook.)

Version Control Trigger:

If Octopus Deploy added a VCS trigger, then it would allow us to use GitOps.

Both of these allow Operations to enable control from check in / merge point in source control.