After my research SignalR is a middleware I can use in ASP. Is it possible to host the server part in for example a console application or a dll?
I've read about SignalR webhost, but the guide is for .Net Framework: https://learn.microsoft.com/de-de/aspnet/signalr/overview/deployment/tutorial-signalr-self-host
Not 100% sure what you are asking.
SignalR is built into ASP.NET core, you can reference and use it within the same application, which can be running in IIS, or self hosted, even asp.net core web apps are basically console apps, but there will need to be a web (internet aspect to your application.
There are also specific Azure services to handle signal R if that helps https://azure.microsoft.com/en-gb/services/signalr-service/