There are a lot of questions in your post. Let’s start from the beginning 
The error you report is unusual. It looks like you are using your application’s domain (localhost:7123) as the authorization server (issuer) domain. This should be your Auth0 domain. Have you configured your Blazor app as described here?
Actually, I really need to use Auth0 with Standalone Blazor ( NOT Server Hosted )
Is there any example with Standalone Blazor available in any BLOG?
A standalone Blazor WASM application is the same as the Server Hosted one. The only difference is the hosting server. In particular, it must take care of HTTP redirections, like for any SPA, but basically the application works the same.
What is your hosting server/service? Azure SWA?
P.S. Talking of HTTP redirections, I wonder if that error comes from the missing route redirection on the server side 