Anki IOS only sync when you press the sync button. Unlike Anki desktop and Anki droid, It automatically syncs itself whenever you open the app (even better when you’re also closing the app, which only takes place on Anki desktop)
Or If Anki IOS already has this feature. Please let me know how to setup 
The main issue is that iOS apps are not closed like desktop ones are. Every time you briefly switch away, that counts as “closing”, so syncing would end up happening at inconvenient times. iOS will only give apps a brief amount of time to run before they are frozen, so if AnkiMobile were to wait for a while, it would not end up being able to sync.
A way around this would be to introduce the ability to sync in the background, but it will mean a redesign of the syncing protocol to handle this, and will take time.
How about automatically sync whenever Ankimobile is open?
That has similar problems - it’s something the user may be doing frequently if they’re jumping back and forth between apps, and it could get in the way.
I understand the complexity of background syncing.
But what about a pop-up (or optional pop-up) to synchronize at the completion of a deck review (where it congratulates you)
I always want to sync them, and I imagine others do as well.
So it would prompt the desired flow
If it were optional, that’s one possibility. Another alternative would be to allow syncing to be assigned to the top bar/a swipe/etc. Would that work for you too?
Yes, anything where it’s on the Congratulations screen as a visual reminder would be wonderful.