There is no support for syncthing on iOS. I managed to get it halfway working on ish, but it’s just not there, so as of now, I use the shellfish ssh app, that allows to sync folders, through WireGuard also.

Note that I use syncthing for the casual read only "important documents", such as ID copies, tax documents, ebooks, etc. I don’t sync photos, movies and such. Most editable documents are in git repos.

I sometimes work on my iPad, and then I use a ssh client or the ish app (a shell, with vim, etc).

I have used this setup for years, and it’s just low friction, low maintenance for me. I have thought about using an own cloud/nextcloud setup, but it’s just too much work for little value. Like running gitlab instead of ssh and git.