I'm not familiar with CaptureOne but if you have not done so already I would advise putting a memory card in the camera even if you are shooting directly to the computer. This might be something specific to do with the software which could be resolved through an update but to know if that is the case you would want to reach out to the developers of CaptureOne.
With a card in the camera, Capture One will not see/recognize a camera as connected (will not tether) The only way is to remove the card and capture images to a computer. I would love to shoot with an option of what was images were saved to where, jpegs v raws etc....but baby steps! Changing the "Release shutter without card" option in the menu does not fix the error message. Photo of viewfinder when connected to Capture One!
There is a decent workaround! Change the "VF display format" (which can be found on the 8th page of the first Menu ((the red camera icon menu - SHOOT8)) to Display 2. This gives the image that you see through THE VIEWFINDER a black frame and keeps the annoying "No card in camera" warning out of the image and less distracting.
While tethering with Capture one, the viewfinder or rear display always display it has no card in the camera, which is a little distracting while shooting. Does anyone else have this problem or know of a fix to stop it!?
Sounds like it is a camera firmware message.
Not sure about the R5, but most Canon cameras have a Menu setting to allow shutter relase without card without a card.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.