unsafely-treat-insecure-origin-as-secure does not seem to work in Edge 81.0.416.34

I am really having difficulties making this flag to work. It is essential for web development. I am having a local app running on http://localhost:3000 trying to access a https resource on localhost:9001 but to no avail.

I always get an error message in the console "Access to XMLHttpRequest at 'https://localhost:9001/api/auth/login' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource."

I have configured the #unsafely-treat-insecure-origin-as-secure flag and also tried a --unsafely-treat-insecure-origin-as-secure startup parameter to msedge.exe.

Please I need help with this. It's making me crazy.