When I run the most recent version of the World Validation .Net core project, clicking on any razor page causes the browser to just download the page (Brave browser, up to date). If I simply change the project to a netcore30 project, it displays the razor pages as expected. Other non-razor pages work as expected.
Finally got around to upgrading it to .NET Core 3.1 by updating the default configuration to match the razor .NET Core template, the other important piece for .NET Core 3 is needing to configure a StartupActivator class:
Since it relies on some magic of only scanning assemblies where the Startup class is defined.