The Telerik UI for ASP.NET AJAX controls are based on the web form paradigm and heavily rely on the web form server lifecycle that is not available in a MVC/Core environment. They also require a ScriptManager which is not available in the razor pages.
If you look for an integration between Telerik and DotVVM, there isn't an official support, but you may find helpful the following information on the Net:
Last but not least you can also check out the Review of Telerik Toolsets for ASP.NET Web Forms and Core blog post and the related whitepaper (also attached here) which compare the ASP.NET Web Forms and ASP.NET Core frameworks and the suites Telerik offer for both of them.