I’ll second this feature request. For what it’s worth, there’s a now-closed request for this very feature, ostensibly implemented in 0.0.18. Yet I’m on Obsidian Mobile 1.0.4, I can’t find any way to create a second app window. As far as I can tell, there’s no Obsidian command that does this, nor do the usual iPadOS UI affordances work (e.g. tapping the application icon while it’s already open). Recommendation: once this is implemented, it should be added to Obsidian Help.
An example use case: I have one window in Split View with a book open on the left side and an Obsidian “inbox note” on the right. I’d like to be able to open a new fullscreen window of Obsidian on another note in the same vault, so I can work on other items without disturbing my in-progress session with that book.