hello and welcome to the forum
this has been discusedd a number of times in the forum.
https://forum.rclone.org/t/rclone-vs-icloud/18180
rclone does not support icloud but supports many other protocols.
if icloud supports webdav/ftp/sftp/http protocols, then rclone can use that.
one possible workaround; if apple makes an app to install on your computer, that mounts icloud as a local drive letter.
rclone could work with that.
could use rclone to download from gphotos and use icloud tool to upload to icloud.