I don't know of any way that you can add flash to a camera mode setting.
Modes are preprogrammed in the camera firmware.

The flash would be of little use anyway.
Depending upon the camera model, the flash usually only illuminates things that are within about 12 feet from the camera.

If you ever watched a football game at night, you will see hundreds of flashes coming from the stands.
All that does is light up the back of the heads of people sitting in the first through 5th rows in front of the camera.
It does not light up the football field.

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