Black circle on the screen when blue tooth head set connected with xs max-ios 13

I have updated iOS 13 three days ago, and when I connected with blue tooth head set for talking and listening music, there is black circle showing on the screen in the middle. Sometime visible and sometimes not. But it is not Assistive Touch, please note.

When blue tooth disconnected it is gone. What should I do to remove I mean not to appear here anymore.