I'm not sure if I understand your question fully but let me try to answer. When you create an Eventarc Pub/Sub trigger for Workflows, the trigger uses a Pub/Sub topic under the covers to deliver messages to Workflows. You want to be able to filter me...

Cloud Run listens for port 8080 by default but you can configure it to listen another port: https://cloud.google.com/run/docs/container-contract#port

Here's an example Dockerfile for .NET 6.0 that works for Cloud Run: https://github.com/meteatamel/cloudrun-tutorial/tree/master/helloworld/csharp/6.0

How long does the script run for? If it's less than 30 seconds, I'd have a Node.js Cloud Function that gets triggered every 30 seconds by Cloud Scheduler, does its job and gets triggered again in the next 30 seconds and so on.

Not directly but you can use Eventarc in the middle to achieve that. I show how here: https://github.com/GoogleCloudPlatform/eventarc-samples/tree/main/eventarc-workflows-integration/eventarc-pubsub