Drag and drop is broken in WebView2 and BlazorWebView. The issues are documented here:
https://github.com/MicrosoftEdge/WebView2Feedback/issues/2805
https://github.com/dotnet/maui/issues/2205
There is a polyfill that works to enable drag and drop here: https://gist.github.com/iain-fraser/01d35885477f4e29a5a638364040d4f2