Canon EOS 90D Advanced User's Manual page 239

High ISO Speed Noise Reduction
This function reduces the noise generated in the image. This function is
especially eff ective when shooting at high ISO speeds. When shooting at
low ISO speeds, the noise in the darker parts of the image (shadow areas)
can further be reduced.
[ M ] Multi Shot Noise Reduction

Applies the noise reduction with higher image quality than [High]. For a
single photo, four shots are taken continuously and aligned and merged
automatically into a single JPEG image.
If the image quality is set to RAW or RAW+JPEG, you cannot set [Multi
Shot Noise Reduction].
1
Select [z: High ISO speed NR].
2
Set the level.
Noise Reduction Settings
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