External webcam device not found by some programs after upgrade to Ubuntu 20.04

Question

Purely as the result of the upgrade from Ubuntu 16 to 20.04LTS, my external webcam is not found by some software any longer.

Situation

1. uname -r says 5.4.0-54-generic (so this answer should not apply)

2. lsusb says: ` Bus 006 Device 007: ID 046d:08d9 Logitech, Inc. QuickCam IM/Connect

3. dmesg says

   [ 2440.365843] usb 6-1: new full-speed USB device number 7 using uhci_hcd  
   [ 2440.577885] usb 6-1: New USB device found, idVendor=046d, idProduct=08d9, bcdDevice= 1.00
   [ 2440.577888] usb 6-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
   [ 2440.580922] gspca_main: gspca_zc3xx-2.14.0 probing 046d:08d9
   [ 2441.795952] input: gspca_zc3xx as /devices/pci0000:00/0000:00:1d.0/usb6/6-1/input/input21
   

4. lsmod says

   ... 
   videobuf2_vmalloc      20480  1 gspca_main
   videobuf2_memops       20480  1 videobuf2_vmalloc
   videobuf2_v4l2         24576  1 gspca_main
   videobuf2_common       49152  2 gspca_main,videobuf2_v4l2
   videodev              225280  4 
   gspca_main,gspca_zc3xx,videobuf2_v4l2,videobuf2_common  
   ...
   

5. file /dev/video0 says /dev/video0: character special (81/0)

6. Cheese 3.34.0 responds from the start with

   

   and Skype even more plainly with

   

However, the web-conferencing system Big Blue Button does work (via Firefox 83.0).

The similar questions suggested seem date back to 2012-2014 and are not current any longer. I found this one closer to my case and used it as a blueprint to collect info, but its solution does not apply here.

Any tip for restoring full functionalities much appreciated.