Canon EOS R6 Mark II Mirrorless Camera with 24-105mm f/4-7.1 Lens - Manual (Page 919)

Viewfinder Brightness
1.
Select [ : Viewfinder brightness].
2.
Turn the < > dial and select either [Auto] or [Manual].
Auto
Press the < > button. Check the effect in the viewfinder while
shooting.
Manual
Turn the < > dial to adjust viewfinder brightness, then press the
< > button. Check the effect in the viewfinder.
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