I keep a “scratch pad” project around for just this sort of thing, and use a layout similar to this one, which is designed to mimic the Scratch Pad feature, but without all of the limitations of the scratch pad.
Particular to this use case, the scratch pad was designed to be a tool that could be opened whenever Scrivener was running, regardless of whether any projects are open. So for Mac users, that is always an option since the menu bar is always there even when projects are closed. On Windows, I proposed they add a universal system tray for Scrivener that could always be running as an option, that would toggle the scratch pad on and off when clicked. Unfortunately that was never made good on, and has been forgotten since then.
But, for me it’s not a major problem because there is nothing unique to the scratch pad feature, that a project window cannot do. Having this project always open, or readily available on the Desktop, is about as good as an “always on” scratch pad would be, and better in other ways.