CommunityToolkit.MVVM Register contain object or class

Question

I want to substitute CommunityToolkit.MVVM for GalaSoft.MvvmLight.

I add "using CommunityToolkit.Mvvm.Messaging;"

GalaSoft.MvvmLight register message code, include a class like this:

MessengerInstance.Register<MetadataMessage>(this, annotation, (m) => HandleMessage(m));

The type of "annotation" is AnnotationViewModel, a kind of ViewModel.

MetadataMessage is a struct:

public struct MetadataMessage
{
    public MetadataMessage(MetadataMessageType type, MetadataValueViewModel value)
    {
        Type = type;
        MetadataValue = value;
    }

    public MetadataMessageType Type { get; set; }

    public MetadataValueViewModel MetadataValue { get; set; }
}

Another GalaSoft.MvvmLight register message code, include an object is:

MessengerInstance.Register<ModelItemModifyMessage<ModelItem>>(this, messengerToken, (model) => ReceiveModelItemMsg(model));

messengerToken is a object, ModelItemModifyMessage<ModelItem> is a struct:

internal struct ModelItemModifyMessage<T> where T : class
{
    internal ModelItemModifyMessage(T source, ModelItemModifyType type, object oldValue)
    {
        Source = source;
        ModifyType = type;
        OldValue = oldValue;
    }
    internal T Source { get; }
    internal object OldValue { get; }

    internal ModelItemModifyType ModifyType { get; }
}

I try to rewrite register message to CommunityToolkit.MVVM like this:

Messenger.Register<MetadataMessage, AnnotationViewModel>(this, annotation, (t, m) => HandleMessage(m));

But it still not find correct method.

I also try to rewrite another register message to CommunityToolkit.MVVM like this:

Messenger.Register<ModelItemModifyMessage<ModelItem>, object>(this, messengerToken, (t, model) => ReceiveModelItemMsg(model));

It showed:

How can I write correct register message code?

Thanks!