Canon EOS R5 Mark II Advanced User's Manual page 269

Merging Multiple Exposures with a JPEG Image
Recorded on the Card
You can select a JPEG image recorded on the card as the first single exposure. The
selected JPEG image will remain intact.
1.
Select [Select image for multi. expo.].
2.
Select the first image.
Turn the < > dial to select the first image, then press <
Select [OK].
The file number of the selected image will be displayed at the bottom of
the screen.
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