Cannot copy from SD card to iCloud

I have 2 TB of space in iCloud, of which I have used less than 75 GB. I have some video data stored on a 256 GB SD card that I am trying to copy from the SD card to iCloud using my MacBook Air under Ventura 13.4.1 using an SD card adapter. No matter what I do (Desktop and Finder, or command line) I keep on getting error messages like the following (e.g. when doing cp -R):

cp: /Volumes/Insta360/DCIM/Camera01//VID_20230801_153704_00_015.insv: No space left on device

df -m provides the following information:

Filesystem     1M-blocks   Used Available Capacity  iused   ifree %iused  Mounted on
/dev/disk3s5      233752 218627        21    100% 1834742  217200   89%   /System/Volumes/Data
/dev/disk4s1      243952 116461    127490     48%  465847  509961   48%   /Volumes/Insta360

It seems to me that cp -R is trying to copy the files to /System/Volumes/Data before sending them to iCloud, and /System/Volumes/Data appears to have run out of nodes. I don't understand why this is, and I don't know how to get around it. Can anyone please tell me how to copy files directly from an external disk (specifically an SD card) to iCloud?