Canon EOS-1D X Mark III Advanced User's Manual page 769

Information Display in Viewfinder
Setting information can be displayed in the viewfinder for these shooting functions: shooting
mode, metering mode, white balance, drive mode, image quality, AF operation, and flicker
detection.
By default, only flicker detection is selected ([ ]).
1.
Select [ : Viewfinder display].
2.
Select [Show/hide in viewfinder].
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