https://learn.microsoft.com/en-us/dotnet/api/system.threading.synchronizationcontext.send?view=netframework-4.8.1&redirectedfrom=MSDN
SynchronizationContext.Send(SendOrPostCallback, Object) Method (System.Threading) | Microsoft Learn
When overridden in a derived class, dispatches a synchronous message to a synchronization context.
sendobjectmethodsystemthreading