Can I host blazor server side using signalr service without using Azure?

Yes, you can host and deploy the blazor server-side application without using Azure but by using AWS or Firebase. Here you can find the steps for hosting the Blazor application using AWS.  For more details reference the links Host the application to AWS and Host the application to Firebase. 

How can I use response caching in Blazor?

You need to add the Response Caching Middleware to the service collection in the startup class. Then, you can configure the app to use the middleware with the UseResponseCaching extension method, which adds the middleware to the Startup.Configure Refer to this thread for more information.

How can I allow only authorized user to access gRPC service?

The Authorize([Authorize]) attribute is used to allow only authorized user to access the service.  Please refer to the documentation for more details: https://learn.microsoft.com/en-us/aspnet/core/grpc/authn-and-authz?view=aspnetcore-7.0#authorize-users-to-access-services-and-service-methods  

How can I implement policy based authorization in Blazor?

The AuthorizeView component supports policy-based authorization. You can use the Policy parameter for policy-based authorization. Policy based authorization in Asp.Net Core The policies are registered in the application Startup classes ConfigureServices method.