This macro directly edits the same markdown file that is seen by Obsidian. Whenever Obsidian Sync is triggered, it sees that this file inside the vault folder has been modified and will sync it, even if the file has never been opened in Obsidian.
Note: At the moment, Obsidian Sync only runs when Obsidian itself is in the foreground.
So you can open Obsidian to bring it to the foreground (any page will do) and trigger synchronisation of all files modified by the macro.