This document will specifically look at the error: ActIveReports 19 has detected one or more running instances of 'WebViewHost' process....
Please refer to the main KB article for this topic Errors with Web Installer for ActiveReports.NET for other errors involving the installer.
For this error, we have found that this process is related Copilot ( what used to be the Microsoft OfficeHub's built-in app) that is messing with the install.
This is similar to how Visual Studio's sometimes causes issues as AR is installed on top of some of these processes.
In the past we found the fix was to use Process Explorer Process Explorer - Sysinternals | Microsoft Learn
Using that, you can locate WebViewHost.exe and kill process and all associated processes in the tree.
After killing this process in Process Explorer you can install ActiveReports without this being an issue.
You may need to refer to the above KB article to resolve issues moving forwards if you have a different one come up after this process.
Victor Stahlman