Deployed Azure WebApp gives 403 - azure

Question

My issue:
When I try access the main URL for my web app, Azure replies with a '403 - You do not have permission to view this directory or page'.
Context:
I have deployed a Python webapp to Azure using the Pipeline/Release on DevOps (Azure Web App Deploy task seems to run successfully with the artifact generated by the Pipeline). I have previously deployed Python Function Apps successfully with a similar pipeline (different app type of course, and sku).
The Kudu SCM page works e.g.,: myapp.scm.azurewebsites.net
All logs seem to indicate the webapp deployment was successful. If I use CMD or Powershell from the SCM, I can see my app.py (for Flask) is in the correct location. The deployment has my requirements under the site packages installed including Flask.
The app runs quite successfully on my local machine via 'flask run', after I activate the virtual environment.
Yet when I try connect to myapp.azurewebsites.net, I get a 403 on the plain route. Anything after it like /test or /myapi returns a 404.
Something I do not see in any of the logs I can access via Kudu is mention of 'gunicorn', which I believe is what Azure uses by default. I just want to see some kind of log output somewhere to show that flask or gunicorn or something has successfully loaded app.py and is listening for incoming connections.
Maybe you do not know why I would get 403's, but you might know where I should be seeing the aforementioned logs.
TIA for any suggestions.
EDIT:
Something to add is that if I enable logs, and connect to the logstream then I do see logs generated as I access Kudu. This suggests some Application & Web Server are running - at least for whatever container runs that side of things.
It even notes the failed connections from Postman for the actual myapp.azurewebsites.net, but has nothing other than a line indicating that there is a 403.
My app has been stripped down to the most bare app.py with no includes other than Flask and routes which simply return a string. Most includes in requirements.txt have also been stripped out.
Still same issue.

Answer 1

I do have an answer after a couple of days worth of pulling my hair out.
Turns out that the 403's were not actually a permissions issue.
az webapp list-runtimes --os windows
The list shows no runtimes available for Python/Flask Web App. This is why I could not find any gunicorn or Flask logs - neither are set up. Azure deployed the artifact's zip and called it a day.
To rectify this, the DevOps Pipeline/Release must run on Linux. The Azure Web App Deploy task, when set to "Web App on Linux", will have Python runtime stacks available. Once selected, these will allow for a startup command to be specified. (Such as flask run --host=0.0.0.0 --port=8000)
Furthermore in azuredeploy.json the "Microsoft.Web/serverfarms" must have a "kind" specified to include "linux". It also requires:
"properties": {"reserved" : true}
Once deployed, logs indicate that docker is being set to an internal port of 8000 while the default 'flask run' which is executed would use 5000.
Ideally: use gunicorn with port mapping but, to get things going, tell flask to use port 8000.