Can you confirm the startup project is the .Server project in the WASM solution?
I'm also attaching a solution I created with the VS extensions and it works fine for me, so you can compare against it (e.g., with a tool like WinMerge to see what is the differences between the project you have that fails, and this one).
The loading sign not disappearing in a WASM app indicates that something fails during loading of the assets and/or a JS error is thrown, but what is the exact error and its cause is hard to tell based on the available information.
If comparing against the sample here does not help, please open a support ticket and send me the sample project that fails so I can have a look at it.
UI for Blazor