Canon EOS R3 Advanced User's Manual page 381

3.
Select [Zebra pattern].
[Zebra 1]: Displays left-slanting stripes around areas of the specified
brightness.
[Zebra 2]: Displays right-slanting stripes over areas that exceed the
specified brightness.
[Zebra 1+2]: Displays both [Zebra 1] and [Zebra 2].
[Zebra 1] display takes precedence where [Zebra 1] and [Zebra 2]
display areas overlap.
4.
Set the level.
Zebra 1 level
Zebra 2 level
Set by turning the < > or < > dial or pressing <
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> up or down.