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.
Edit: easy to replicate, visit http://validation.web-app.io/ and click on any link to a razor based page.