Starting today, I am unable to Sign In in AppStudio with my ArcGIS Online account. I tried uninstalling and re-installing AppStudio but that made no difference. Before today I had no issue signing in.
The sign-in prompt comes up, I enter my credentials and click "Sign In", and the prompt disappears but then nothing happens; the busy indicator in AppStudio just keeps spinning. I even intercepted the web traffic and it is able to successfully make the request to ArcGIS Online and the authentication tokens are returned.
App Studio 5.4.142 on Windows 10 (OS Build 19044.1889)