Canon EOS M6 Mark II Advanced User's Manual page 109

If the lowest f/number blinks, it indicates underexposure.
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Turn the <6> dial to set a slower shutter speed until the aperture stops
blinking or set a higher ISO speed.
If the highest f/number blinks, it indicates overexposure.
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Turn the <6> dial to set a faster shutter speed until the aperture stops
blinking or set a lower ISO speed.
Shutter Speed Display
For example, "0"5" indicates 0.5 sec. and "15"", 15 sec.
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Shutter-priority AE Mode (Tv)
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