The R5 can transfer images to an FTP server. Based on a little Googling, it looks like Dropbox does not support FTP. So I think you're out of luck.
You could use image.canon, or use a file-sharing service which supports FTP connections. I haven't tried either of those, but they seem like your best options.
Additionally, If you are not trying to do this remotely (and in one step), you can transfer images directly to a PC with a dropbox client installed, these will then sync to the cloud.
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12/05/2023: New firmware updates are available.
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.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.