Hi @M. Vaihinger ,
Thank you so much for your patience. You are seeing a 0 for this metric because the Thread Count metric in Azure App Service is not currently supported for Linux App Services.
The Thread Count metric is only supported for Windows App Services. For Linux App Services, you can use other metrics such as CPU usage, memory usage, and request count to monitor the performance of your app.
I have shared your feedback with the doc team so that the document you shared can be update with a note that states Thread Count metric is not supported for Linux App Services. You can track it here: https://github.com/MicrosoftDocs/azure-docs/issues/109002
Hope that helps. please let us know if you have further questions or feedback.