Canon EOS RP Instruction Manual page 328

Setting Cropping/Aspect Ratio
Setting examples
Y set
U set or EF-S lens
used
W set
120
3
Take the picture.
When [1.6x (crop)] is set or an EF-S
z
lens is used, an image magnified
approx. 1.6x is displayed.
When [1:1 (aspect ratio)], [4:3 (aspect
z
ratio)], or [16:9 (aspect ratio)] is set,
the image within the black masked is
captured.