I recently noticed that my nextcloud instance was missing photos. I have the android app set to automatically upload my photos. When I need to clear up space on my phone, I make a separate backup (because I’m a paranoid SOB and hard drives are relatively cheap). I noticed that nextcloud auto upload missed about 10% of the photos. I’m not going to bash the nextcloud devs, as I recognize that I am using a free product and am owed nothing, but I’m making this post so others are aware of this risk. Apparently I’m not alone https://help.nextcloud.com/t/android-client-does-not-auto-upload-all-images/216849/14
Syncthing or Resilio Sync for photo/file backup from phone. Both work amazingly well.
Sun thing for me was absolutely terrible. If I recall correctly, huge pain in the ass because I vlan off my wifi and had to mess with policies for discovery. I found the app would often freeze and lock up, glitch, etc. And this was on two different phones.