Ecco la risposta ufficiale in merito ad IdentityServer nei template di ASP.NET Core.

Per chi la volesse leggere:
https://devblogs.microsoft.com/aspnet/asp-net-core-6-and-authentication-servers/
https://github.com/dotnet/aspnetcore/issues/32494

Alcune alternative:
https://azure.microsoft.com/en-us/services/active-directory/
https://github.com/openiddict/openiddict-core
https://www.keycloak.org/
https://wso2.com/
https://auth0.com/