Canon EOS R3 Advanced User's Manual page 351

Note
To obtain better performance with the card, formatting the card with the camera
before recording movies is recommended (
Movies cannot be recorded in HD or VGA quality.
4K Movie Recording
Recording 4K movies requires a stable card with a fast writing speed. For details, see
Cards That Can Record
4K or High Frame Rate movie recording greatly increases the processing load, which
may increase the internal camera temperature faster or higher than for regular movies. If
[ ] or a red [
stop recording the movie and let the camera cool down before removing the card.
(Do not remove the card immediately.)
From a 4K movie, you can select any frame to save to the card as a JPEG still image
( ).
Movies.
] icon appears during movie recording, the card may be hot, so
).
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