Frustratingly, support for Google Photos in rclone is handicapped by the limitations of the Google Photos API: you can't download Photos at original resolution. This is documented on your second link.
That's unfortunate ... and I believe there are some other end-user ("consumer") products that also interfere with the direct mechanism that 'rclone' uses to request data.
> NB The Google Photos API which rclone uses has quite a few limitations, so please read the limitations[0] section carefully to make sure it is suitable for your use.
For anyone intending to use rclone to download their photos from Google Photos, be aware that you will lose EXIF data. If you download videos, they will be lower quality. There are more limitations in the link.
If they have a Mac, then yes. You can enable download of all full-resolution photos from iCloud to a Photos library which can be stored anywhere and is stored in a standard directory structure.
In fact, most of them are not files in a directory - that's what makes most of the rclone use-cases so impressive. If they can interact with gdrive/photos/S3/etc. they should be able to interact with iCloud Photos ...
Without installing rclone and without using any of your own bandwidth, you should be able to:
Or maybe you just want to keep a copy in your rsync.net account: [1] https://rclone.org[2] https://rclone.org/googlephotos/