I found a solution that seems to be working as expected.

Briefly, after the default installation of DevOps Express, from IIS I:

• deleted the Web Site composed of the two applications: "DevOps" and "queue";
• created a new web application, "DevOps", under the default web site, then according to the initial installation scheme I added "queue" under "DevOps".
• set the Basic Authentication on the "DevOps" web application.

The error I reported in my previous attempt (as stated in my help request) "Could not load file or assembly.... HRESULT: 0x80131040", was due to a dirty installation in the default application associated with the default web site, I have now deleted.

Now step by step....

Here the IIS state from defaut DevOps installation

After deleting the Web Site installed with default setup: I delete "Azure DevOps Server", note "DevOps" app must use his Application Pool and so also "queue"

At least enable Basic Authentication: Setting basic authentication

Hope this will help someone, of course considerations and suggestions are wellcome