Canon EOS R3 Advanced User's Manual page 150

2.
Set the image size.
Standard/Auto switch card/Record to multiple
For RAW images, turn the <
JPEG/HEIF images, turn the <
Press <
Record separately
When [
[Rec. separately], turn the <
< >. Note that recording separately to
available for RAW images.
Select an image size on the screen displayed, then press <
> to set it.
Rec options] in [ : Record func+card/folder sel.] is set to
150
> dial to select the size, and for
> dial.
> dial to select [ ] or [
and
], then press
is not
>.