I just want to add a little tip, since I, too, use iA Writer with Obsidian. iA Writer on iOS has a “custom keyboard” that you can tweak. I put the bracket symbols in a prominent, easy-to-reach location on this keyboard to help me write wikilinks when capturing ideas on mobile. It doesn’t auto-complete filenames but it saves time.
And for what it’s worth, placing my Obsidian vault in iA’s folder in iCloud has been seamless for me.