In regards to the Desktop App Web Viewer, this is the process that allows the App for outlook and many other apps in outlook to open and run. This has recently had some issues with performance however and the Office team is now deploying a new process called WebView2. Currently this has been deployed to the Production channel, 50% of Current Channel and will be deployed to the Monthly Enterprise channel on 4/14/2021.
If you open up outlook > click file > account settings > you will see whether you are on the Production channel, Current channel or Monthly Enterprise Channel.
You could also install the webview2 runtime here: Webview2 – Microsoft Edge Developer
This issue would be likely be present in any app that is trying to be deployed from Outlook. Could you show a screenshot of the credential prompt? And are you using Exchange Online or Exchange on-prem?