Long story short the error is caused by old Radzen.Blazor.js. Using a cache buster such as the version of the Radzen.Blazor assembly is the recommended approach.
<script src="_content/Radzen.Blazor/Radzen.Blazor.js?v=@(typeof(Radzen.Colors).Assembly.GetName().Version)"></script>
I am closing this thread as there isn't much more to add to it.