If you are developing an API, for authentication, you should use:

builder.Services.AddKeycloakWebApiAuthentication(builder.Configuration);

For a web app, use:

builder.Services.AddKeycloakWebAppAuthentication(builder.Configuration);

For authorization, use:

builder.Services.AddKeycloakAuthorization().AddAuthorizationServer(configuration);

You can follow the migration guide below:

Source:https://nikiforovall.github.io/keycloak-authorization-services-dotnet/migration.html