Intel Mac mini 2018 recognises Logitech C920HD but no picture

Anybody ever get to the bottom of this Logitech / Apple (non)problem? Tried all the suggestions with no joy.

Running OS X 11.5.2 Big Sur. System Report shows the camera, both plugged direct into the USB on the mini and via a USB powered hub.

USB data shows Camera OK and current available and taken as 480mA.

The only data which is not available to me is the Gb./sec. throughput required by the camera.

The mini specs say that the USB-A ports are good for up to 5Gb./sec.

Help sincerely requested.