Lets start with some basic stuff. First....It appears it works OK when using a Component signal source fine, is this correct?
If so, try using a different HDMI source, like a DVD player/HDMI out from your computer.
"Just an aside, when I look at "Bluetooth or other devices" or "devices and printers" within Windows 10 I only see "roxio video capture USB" as an audio device. Is that correct? "
Are you seeing this as well as the 2 devices in " sound video and game controllers" .
You have got the right drivers,so tell us how you have got your VCR hooked up to your capture device...details.
User guide https://www.roxio.com/static/roxio/docs/guides/gsg/VHStoDVD3/Easy_VHS_to_DVD_GSG_ENU.pdf
The problem is created when you plug in the Capture USB device before you install the software.
Plug in the USB device, (in Device Manager), Disable/Uninstall the driver, remove the USB device and hide it.
Then reboot and run a Repair with the software.
To get the serial number go to the main Roxio website https://www.roxio.com/en/ .
Select MY Account (top right)>Log in with you Email address and password, and your Registered Product(s) should be there.