Canon EOS M Instruction Manual page 135

Flash can also be used (with Speedlite 90EX attached).
Since the flash will require recycling time, the continuous shooting
speed will be slower.
When the battery level is low, the continuous shooting speed will become
slightly slower.
The continuous shooting speed may become slower depending on the lens
type, shutter speed, aperture, subject conditions, brightness, flash use, etc.
When you use a Creative Filter and shoot, even if you set the drive mode
to <i> (continuous shooting), single shooting will take effect.
i Continuous Shooting
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