Are you trying to save a file from Shortcuts or a file from Scriptable?
Shortcuts can save files to any folder, but if you want it automatic, then it would need to be within the Shortcuts folder structure.
Scriptable can create file system bookmarks, but the bookmarks are for use in Scriptable (either standalone or via the Shortcuts calling); but that isn’t the same as making such a bookmark available for Shortcuts to us, only Scriptable when triggered from Shortcuts.
At least that’s my current understanding.