Just upgraded and get the following:
In the latest version we have fixed a problem with JS interop not working in design-time. This caused various problems. The fix however seems to break for you because a very old version of Radzen.Blazor.js seems to be cached. Try the following as a fix. Open your _Host.cshtml or App.cshtml file and replace
<script src="_content/Radzen.Blazor/Radzen.Blazor.js"></script>
with this:
<script src="_content/Radzen.Blazor/Radzen.Blazor.js?v=@(typeof(Radzen.Colors).Assembly.GetName().Version)"></script>
Sorry tried both, same problem. Also cleaned and rebuilt the solution, but it's still there. App runs perfectly, just can't use the visual editor.
We will need your application to see why this problem occurs.
You should also be able to use design time for the other components. You can select the RadzenDataGrid from the screenshot and set properties.