I prefer SyncThing on both mobile and desktop devices. It's open source and mature, the server only makes devices findable between each other. It allows 1 or 2 way sync. And it has advanced settings for keeping removed files (e.g. trashbin that cleans anything older than X days.)
How to backup iCloud photos? I have an iPhone and Windows as desktop.
- Go to https://privacy.apple.com - Choose "Request a copy of your data" - Select iCloud Photos
After a few days you'll receive a download link to the full iCloud Photos library. Perhaps only available in EU (it's a GDPR-mandated feature).