This code reproduces an issue in Blazor Server (.NET 5) where switching the environment away from development causes the application to lose the BlazorApp10.style.css file.
Run the code in Kestrel. It will work fine. Then, launch it in IIS Express. The styling will be missing, including the menu, because the BlazorApp10.style.css file is missing (404 error).
This is a stock Blazor Server (.NET 5) template with only one change - I set the IIS Express ASPNETCORE_ENVIRONMENT variable to "Production". No other changes were made to the template.