Removed backports.zoneinfo dependency which breaks Python 3.9 support and not even needed with default Python 3.8 in DSM7.2.
Repackaged latest official iCloud Photos Downloader release instead of building from sources:
https://github.com/icloud-photos-downloader/icloud_photos_downloader/releases/tag/v1.17.3
Note, with the latest release requires /tmp directory to be mounted with exec flag.
sudo mount /tmp -o remount,exec
More information at icloud-photos-downloader#764.