The biggest gap I've noticed in SyncThing right now is that their iOS client doesn't work well. It's a third party solution you have to pay for, and it can't sync into app folders or the new iOS file paradigm introduced in recent versions of iOS.
I guess you’re talking about the client “Möbius Sync”. I’ll add that it’s also not available in most countries, for some reason the developer restricted it in the App Store.
I'd love to switch over to SyncThing, but it would be next to useless on my iPad Pro, so I'm stuck using the incredibly buggy NextCloud filesync solution.
After reading this, I did some digging, and found Mobius[1]. It seems to work really well, I just got the pro version. I think the last time I looked, I saw that Syncthing only officially had an android client and stopped looking after that.
To be fair, I still would really like an official, open source iOS client, instead of some closed source thing I need to trust; I'm still a bit uneasy about using it.
