I just learned about mem.ai, which is another note app based on links. At least for Mac users, it includes a Spotlight-equivalent, where you press ⇧⌘+Space, and a pop-up appears for either searching old notes, or writing a new one.
This is pretty much precisely the functionality I was looking for when I started this thread.
Unlike Obsidian, it keeps all your writing internally, so you can’t access your notes except through the app. For that reason, I’m probably staying with Obsidian, but it would be super super cool to see this functionality added on!