Can I change the call screen layout regarding my requirement?
Currently, you can remove the default buttons and add your own custom buttons. Can you please let us know what exactly are your requirements?
how to customize ‘select output audio/video source’?
As I mentioned in my previous reply. Currently, only the default buttons can be customized. I have created a feature request for this and added you to the same. You will get an update via email if/when the product team decides to take this up. You can check the feature request here.
Can you please elaborate more on what exactly you are trying to achieve? If you can, please share a screenshot of what you are trying to achieve.
Thank You for your support