Canon EOS R5 Advanced User's Manual page 479

Caution
Voice memos cannot be added to movies or protected images.
Voice memos cannot be recorded with an external microphone.
Note
Audio quality of voice memo recording can be changed in [
quality].
To record voice memos longer than 30 sec., repeat step 3.
You can record a single voice memo during image review (immediately after
shooting) by following step 3.
Even during transfer to an FTP server, you can add a voice memo to images from
the playback screen. However, voice memos cannot be added to the image
currently being transferred.
479
: Memo audio