Can I trust iOS background sync?

Im looking for EU based alternatives for iCloud with security and privacy in focus.

Im trying out Jottacloud but something I cant test right away is the reliability of the background sync. I basically want it to work without every worrying about sync photos.

I've read this and it doesnt seem promising:
https://docs.jottacloud.com/en/articles/2233504-background-uploads-on-ios

I've read a comment from a zeitkapsl dev, that says reliable sync is indeed possible:

https://www.reddit.com/r/BuyFromEU/comments/1q3qesk/comment/ny2zjzm/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

So; is that something Jottacloud is working on in order to guarantee this?