Canon EOS R5 Advanced User's Manual page 160

Caution
Expanded ISO speeds (L, H) are not available in HDR shooting.
Some scenes may look different from how they appear on an HDR display device.
Histograms of images captured with [HDR shooting ] set to [Enable] are
not based on images as converted for HDR assist display. Image areas shown in
gray in the histogram roughly indicate signal values that are not used.
[ : Disp. performance] is not available when [HDR shooting ] is set to
[Enable]. It is set to [Smooth].
For images captured with [HDR shooting ] set to [Enable], before
playback on an HDR display device, set [ : HDMI HDR output] to [On] ( ).
Note that regardless of the [HDMI HDR output] setting, HDR images are used for
Live View display on HDR display devices.
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