Canon EOS RP Instruction Manual page 368

Setting Noise Reduction
With [Auto] or [Enable] set, the noise reduction process after the picture is
o
taken may take the same amount of time as that for the exposure.
Images may look grainier with the [Enable] setting than with the [Disable] or
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[Auto] setting.
[BUSY] is displayed as noise is reduced, and the shooting screen is not
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displayed until processing is finished, when you can shoot again.
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