breaking change from MVVMLight? <TMessage> cannot be Value type (ex. Guid)

[bwjunkie]

mvvmLight allowed
Messenger.Register<Guid>(...
CommunityToolkit error:
Type argument 'Guid' does not satisfy the Class constraint for type parameter TMessage

Question: is this a breaking change from mvvmlight (which must have a different implementation of TMessage?)

note: the migration documentation : https://learn.microsoft.com/en-us/dotnet/communitytoolkit/mvvm/migratingfrommvvmlight#migrating-observableobject

// MvvmLight
Messenger.Default.Register<MyMessage>(this, this.OnMyMessageReceived);

// MVVM Toolkit
Messenger.Register<MyViewModel, MyMessage>(this, static (r, m) => r.OnMyMessageReceived(m));

thank you
Josh