Hi - yes, as Søren says for V9 we're only supporting storage of Forms in the database. The docs for this are here, which links off to a page detailing how to enable this in V8.

For discussion on the reasons why we made this change, please also see here.

You've found the only method signature change - we did this just as the previous one was a little odd (in that RecordEventArgs also held details of the Record, and felt we could improve the naming). There's an example with the new syntax here.

With Umbraco V9 doing less type scanning, you'll also need to register your new workflow. The core ones are done in an extension method on IUmbracoBuilder:

public static IUmbracoBuilder AddUmbracoForms(this IUmbracoBuilder builder)
{
    // omitting all but the workflow registrations...

    builder.WithCollectionBuilder<WorkflowCollectionBuilder>()
        .Add<ChangeRecordState>()
        .Add<PostAsXml>()
        .Add<PostToUrl>()
        .Add<SaveAsFile>()
        .Add<SaveAsUmbracoNode>()
        .Add<SendEmail>()
        .Add<SendRazorEmail>()
        .Add<SendXsltEmail>()
        .Add<Slack>()
        .Add<SlackV2>();

    return builder;
}

Which we call from a composer (but if you prefer you could call the extension method from StartUp:

public class UmbracoFormsComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder) => builder.AddUmbracoForms();
}

So you will need to do something similar for your workflow type.

This last part I've realised isn't documented - other than now here I guess - so I'll make sure we add that.

Hope that helps.

Andy