Hey Rick – there isn’t a guide, but I’ve successfully used dffs on SharePoint Online for the past year and half. Start with installing the Modern CEWP in the top links. You may have to enable custom scripting in the admin center. I think he has that information on here also, but if you search online you’ll find it (I didn’t use powershell). Then I just set up the installer like you normally do. You may have to turn on web part pages in settings if you don’t see it. You can use the modern experience on the lists if you want, but most of the time I use classic so I can customize the view to my liking.
I know Alexander is working on something more specific for modern SharePoint, but I’ve been able to use it mostly as it worked before.