I would not change .NET Core to force initilialize the main thread to MTA by default like it is done in .NET Framework.
.NET Core startup is much simpler and it does not need COM initialized to do what it needs to do.

https://github.com/dotnet/coreclr/issues/13688#issuecomment-326759385

Что делать — тоже в той ветке написано:
Thread.CurrentThread.SetApartmentState(ApartmentState.MTA);
ну или TrySetApartmentState

I would not change .NET Core to force initilialize the main thread to MTA by default like it is done in .NET Framework.
.NET Core startup is much simpler and it does not need COM initialized to do what it needs to do.

https://github.com/dotnet/coreclr/issues/13688#issuecomment-326759385

Что делать — тоже в той ветке написано:
Thread.CurrentThread.SetApartmentState(ApartmentState.MTA);
ну или TrySetApartmentState

> Указание атрибута [MTAThread] не помогает.

это странно.