I've been trying to find ways to get SignalR Core working correctly with Godot, and it has been extremely painful to figure out how. Classic .NET SignalR can't connect to a SignalR Core server (nor vice versa) and I get all kinds of weird build issues any time I try to use the SignalR Core libraries together with Mono. Even though Mono supports .net standard 2.0 and 2.1, there seems to be some sort of compatability issue between the two. I am currently writing a wrapper library in .netstandard 2.1 to see if I can fix this, but so far it's been hell to debug. I'll let you know what I find.