I tried using Obsidian on iOS and lowkey hated it. On the iPhone, the interface gets in the way as it’s clearly not designed for a small screen. On the iPad, Obsidian doesn’t mesh well with the external keyboard as it ignores the iPadOS conventions. So I started to look for a companion app.
I settled on Taio: it’s less known but surprisingly feature-rich. It’s pretty much compatible with Obsidian and handles some differences well (e.g., it can’t display PDFs within a note but it will still recognize ![[this notation]] as a link and will open the PDF in a new tab if clicked. It also has built-in PDF annotation tools.) It supports Wikilinks and pipe links, and it can add any iCloud folders to its library so you can point it to your existing Obsidian vault without having to move it or anything. The only thing you’re going to miss is if you’re using any very divergent plugins like Dataview, for obvious reasons.
And recently, iA Writer added support to Wikilinks, and I’ve been testing it with positive impressions. The main downside is that it doesn’t support PDF preview in any shape or form.