Canon EOS REBEL T8i Advanced User's Manual page 150

Caution
If the "30"" shutter speed blinks, it indicates underexposure.
Turn the <
shutter speed blinking stops or set a higher ISO speed.
If the "4000" shutter speed blinks, it indicates overexposure.
Turn the <
shutter speed blinking stops or set a lower ISO speed.
Note
Aperture value display
The higher the f/number, the smaller the aperture opening will be. The f/number
displayed varies depending on the lens. If no lens is attached to the camera, "00"
will be displayed for the aperture.
> dial to decrease the aperture value (open the aperture) until the
> dial to increase aperture value (close the aperture) until the
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