it doesn’t exist but could be done with a custom app. I have looked into this topic a while ago already.
Although I would also consider using an external workflow engine and write a connector for it. Camunda (open source) for example has a good example for a invoice approval process, which in their example uses a box[.]com connector.
This example, which is open source, could be adapted for Nextcloud (writing a Nextcloud connector). Benefit is that this whole process management, forms, UI, etc. would all be provided with a very simple and clean web UI.
It’s open source:
And if you want, you could even read in all pending taks / processes via Camunda REST API and display a list of pending tasks within a Nextcloud app itself (which works as a view only but links to the tasks on the workflow engine UI then.)
I see either Camunda or Flowable as good options to achieve document-driven workflows, especially when they become a bit more complex.
Need to consider that Nextcloud is not an ECM but a EFSS system, so it’s coming from a different side. Using a workflow engine with standardized BPMN models and a connector will keep separation of concerns really clean, each system focussing on it’s core strength.