It's not clear to me whether .NET 6 (and therefore C# support) is going to make 4.0 freeze. It's really just been one guy working on the dotnet6 branch, which is unfortunate. I'm really excited for many features of Godot 4, and GDScript is perfectly adequate for UI glue code and stuff, but to write a serious game you really want C#.
The Wiki page says it already supports C#. As completely on the outside, what is missing?
IIRC (and this could be wrong / have changed since I last looked into it) the idea was to re-work this in Godot 4 to provide more like bindings, so that users could opt to use Mono, .NET 6, CoreCLR, NativeAOT, or whatever version they preferred.