I know that sync is not possible on close but can it at least happen when the app is opened (maybe when it is switched to from another app too?) ideally this could be toggled.
Also I don’t know if this will work but is it possible to make an automatic small sync like ankiweb website does (I think?) whenever you answer a question or make a change to a card.
I recently bought ankimobile because I wanted to suspend and bury cards and (re)build filtered decks from my phone without having to open my laptop. I was thinking about just using ankiweb for reviews and switch to ankimobile if I wanted to do something but I think that this would still be difficult (I haven’t tried it yet, I think I can deal with ankimobile sync for some time at least)