Here is the link to the official Microsoft .Net 8 Runtime for x64 (Windows) needed for SolmanSolitaire version 6  

Download .NET 8.0 Desktop Runtime (v8.0.6) - Windows x64 Installer (microsoft.com)

You can also just browse "Microsoft .Net 8 Runtime" and looking for the windows x64 installer (not the Sdk version) from Microsoft.

Required for version 6 of SolmanSolitaire, available on Windows 11 only.