Gary
Thanks for your comments. I appreciate the help.
I looked for assistance from Lidl/Silvercrest to no avail, so I've decided to take it back and get a Mac-suitable video grabber through Amazon. I'll also upgrade my Mac OS which I am continually reminded is a bit dated!
In the file, depending on the kernel version, drivers/media/video/cx231xx/cx231xx-cards.c or drivers/media/usb/cx231xx/cx231xx-cards.c go to struct usb_device_id cx231xx_id_table[] and add these two lines e.g. at the beginning of the definition:
Silvercrest Usb 2.0 Video Grabber Vg 2010 Drivers Download