Update regarding problems stated earlier
A)
We found the solution: https://github.com/PX4/Firmware/issues/13416
It is a gstreamer related issue. We solved it by running:
sudo apt install libgstreamer1.0-dev
sudo apt install gstreamer1.0-plugins-good
sudo apt install gstreamer1.0-plugins-bad
sudo apt install gstreamer1.0-plugins-ugly
B) not resolved