Since this is a User repository, it is not possible to configure Pages to use a different source repository than master. So I had to update my workflow and set development as main branch.
Another option might be pushing the artifacts to a separate repository and have Pages configured there.
The deployment is handled by a GitHub action workflow that will
- setup .NET
- build the application and publish it to the
/build/folder - uses JamesIves/github-pages-deploy-action to deploy the code to the
masterbranch