GNOME Text Editor will automatically save every unsaved file. This folder is located in the application data directory (~/.local/share/gnome-text-editor or in the respective flatpak folder). You should normally not care about that folder as every draft file is always accessible via the Open menu.

You can identify a draft in the title of GNOME Text Editor. There is a subtitle 'Draft' if your current document is not saved and will reside in the draft folder.