... is there any possibility as a teacher to click submit for him...?
I do not think so. But, in the quiz settings, if you set a "Close the quiz" time and/or a "Time limit", and if you set "When time expires" to "Open attempts are submitted automatically", the quizzes will be submitted automatically even if students forget to click the "Finish attempt" / "Submit all and finish" buttons.
...to cancel his quiz if he turn off camera and keeps working in quiz?
You can always cancel a quiz after it is finished. If you want to cancel the quiz while it is running, set a "User override" for the student with the "Cloze the quiz" time enabled and set to a previous time.