Hi Roger,
I am Sumit, an Independent Advisor and a 3 year Windows Insider MVP here to help.
Windows 10 2004 is currently in seeker mode - if you manually press check for updates it gets downloaded. Are you sure it rolled down automatically to your device?
As it is >1 month since the availability, upgrading right now isn't a good idea. That's something I would explain later on, if needed.
In your case, if the data and apps are in large amounts, the update may take time. If you want to cancel it, click Pause updates for 7 days option.