This would be great to get merged in. Supports older .NET Framework and very current .NET (Core). I'm hitting an exception of:

System.PlatformNotSupportedException: Operation is not supported on this platform.
   at System.Action`4.BeginInvoke(T1 arg1, T2 arg2, T3 arg3, T4 arg4, AsyncCallback callback, Object object)
   at WebSocketSharp.WebSocket.closeAsync(CloseEventArgs e, Boolean send, Boolean receive, Boolean received)
   at WebSocketSharp.WebSocket.CloseAsync(CloseStatusCode code)

Which is caused due to the outdated BeginInvoke usages.

I notice all these other issues mentioned the same problem. Maybe it's time for a fix?

#412
#473
#487
#601
#652

@sta any updates?

I'd like to add in my vote for this - I recently upgraded a project that I rely on to .net 6 and am running into issues.

I think it's now between updating backward compatibility only or moving to the newer compatibility but losing older device support.

Or possibly updating both versions simultaneously in the future. Not all devices or IDE's support Net6 yet unfortunately. Maybe another 5-10 years.