issue can be reproduced by widget-based camera example that uses QCamera.
To force QCamera not to start correctly, one can launch Windows built-in Camera app first. Then start camera example.

At first, one will be greeted by a warning message which is either "Hardware MFT failed to start streaming due to lack of hardware resources" (6.5) or "Streaming error" (6.4), which is as expected because we force it to.

Close the warning message and File->Stop Camera. QCamera of 6.4 stops properly and application itself still runs. But QCamera of 6.5 does not and crashes the application. Application stays unresponsive and one has to kill it.