Jitsi cannot access webcam, other programs do


I am new here and i am new with Linux / Lubuntu. Jitsi is running on an old MSI Wind U-100. Of course it needs long time to start up the Jitsi Desktop program. But then it should work well. It connects with the built in microphone but does not to the built in webcam. The webcam is a NB-Pro BisonCam.

It can be operated with other programs like GucView at a frame rate of only 15 fps @ 680 x 420 px and a red LED light will be on, while camera is active.
When I want to operate the webcam with Jitsi, this LED keeps dark.

In the meantime, while I was waiting for a reply here, I have tried a separate webcam via USB. It is a Logitech C270. But this camera was also detected by Jitsi client, because it showed up in its drop down device list, but also Jitsi could not aktivate / switch on the camera.
Now we know, that it is not a question of camera or its device driver, but of the lack of Jitsi, to be able to activate the camera on Lubuntu.

Tech-data: Lubuntu 18.04 - 32bit default installation on MSI Notebook with N270 CPU (Atom), 32-bit, 1 core 2 threads, 2GB RAM

What can I do, to let Jitsi detect and activate the webcam?