Video source not visible while video selection settings are displayed

### Your use case

#### What would you like to do?
As a video call participant,
I would like to select the best video source
And verify the source by looking at the video image

#### Why would you like to do it?
I go to the settings and video and switch the sources

#### How would you like to achieve it?
The video image is not visible as the dialog sits over the video image


### Have you considered any alternatives?

I have not found an alternative.

### Additional context

Other video conferencing software offers source selection, either
- with a preview image at the source selection point
- as a menu choice from the buttons below the main video screen, so that the main image is not hidden

No file or test is named in the issue. Search the repository for the video settings dialog and source-selection UI, then run the relevant tests you find; done means participants can view the selected video source while choosing sources without the settings dialog obscuring the image.

Written by the indexing model from the issue text.