For a long time, I’ve used Drafts for quick capture on my iPhone. I haven’t yet found a way to get notes from Drafts into Obsidian. Drafts can’t save directly to Obsidian Sync, for obvious reasons, and doesn’t have access to Obsidian’s folder if iCloud Drive is used for syncing.
Yes the same URI scheme works on both iOS and desktop/laptop (I think it assumes you have at one point opened the same vault on both). Here’s what I use, though I forget where I got it from: