Hello I have updated radzen to version 3.0.1 and after that I got a similar error in google console :
DevTools failed to load SourceMap: Could not load content for https://localhost:44344/_content/Radzen.Blazor/css/themes\default.css.map: HTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILURE
Yes, source map is not available for the themes css and we will remove the declaration from the source in the next update.