Canon EOS 80D - Manual (Page 74)

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If you set this function, <G> will appear in the viewfinder when
the camera detects flicker caused by the blinking of the light source. By
default, flicker detection is set to [Show].
1
Select [Viewfinder display].
 Under the [52] tab, select
[Viewfinder display], then press
<0>.
2
Select [Flicker detection].
3
Select [Show].
Displaying the Flicker DetectionN
If you set [z4: Anti-flicker shoot.] to [Enable], you can shoot with
reduced unevenness of exposure caused by the flicker (p.179).