Microsoft released a new version of the webview2 runtime that modified the STS token response that Bentley gets back in CONNECTION Client, changing it from a pure XML response (that CONNECTION Client can parse), to an HTML response (that CONNECTION Client cannot parse). This only manifests itself in the old CONNECTION Client versions (v23.x and below). The problematic WebView2 version was released 8/7/25 - Version 139.0.3405.86.
The issue manifested itself with existing older versions of CONNECTION Client, it was not triggered by installation of any new Bentley software. It was the result of an upgrade from Microsoft.
Moving to the latest CONNECTION Client version (version 24.01.00.23 or above uses OIDC authentication protocol for communication with Bentley Cloud Services and do not suffer from this issue) will resolve this issue.
Please update to the newest CONNECTION Client 25.00.01.14 by using the download link -
https://www.bentley.com/software/connection-client/