Themes don't seem to be working

[fullreboot]

Describe the bug

Using themes does not seem to work at all, even after following the instructional video. Are themes still loaded the same? Previously it looks like it was an angular app, now themes are attempting to be loaded from a theme-dependent index.cshtml file. It produces the error seen below

return View($"~/Views/Themes/{model.Blog.Theme}/Index.cshtml", model);

Screenshots

Additional context

[chatay]

Hello, can you please explain the steps you apply? exactly at which stage you get this error?