I cannot stop or delete versions of a project created as it was created as a flexible environment within the EU. I understand the restriction by region but cannot work out w
You have to have at least one version for the default module. That's the reason why it doesn't allow you to delete it.
You need to deploy a new version, it can be a Flexible VM (deployed to another region in your situation), or Standard VM.
As a workaround, when you don't have any app to replace it right now, you can deploy an empty app instead. You have to create an app.yaml:
---
runtime: python38
handlers:
- url: /
script: auto
and deploy it using:
gcloud app deploy app.yaml
As your app.yaml doesn't have any script to execute, you'll not be charged for any instance.