Canon EOS R5 Mark II Advanced User's Manual page 970

Auto Reset
For restarting file numbering from 0001 after switching cards or
creating folders
File numbering is reset to 0001 if you replace a card, create a folder, or switch the target
card (as in → ). This is useful if you want to organize images by cards or folders.
Note that file numbering may continue from any existing images in cards or folders that you
switch to. If you want to save images with the file numbering starting from 0001, use a newly
formatted card each time.
File numbering after replacing cards or switching target cards
Card A ( )
Card B ( )
(1) File numbering is reset
File numbering after creating a folder
Card A
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