I use https://github.com/icloud-photos-downloader/icloud_photos_do... running on my NAS to regularly download photos from my wife's iCloud account. The photos are stored in full resolution on iCloud with the EXIF data, unlike Google Photos, so that's nice. The only annoyance is that you need to reauthorize the tool every three months. But it sends you a reminder when the time is coming up.
Beware that edits, portraits and some custom photo modes aren't currently downloaded. And modifying an edit twice or more will not sync. (no modtime or chksum)
