Happy to open another issue so as to not hijack this one, but I would also personally settle for defaulting to the Desktop directory (or, if not truly defaulting, then allowing the addition of a config option to specify a default directory).
The way Geany works right now (having checked on Windows 10, in particular), is if you call for a 'Save' or 'Save as' from a new file, there is no obvious way to save the file without moving a hand off the home row and using a pointing device. I'd like to 'Save as', type a new file name, and hit enter. I do not want to move a hand away from the keyboard to a mouse pointer just so I can save a file at all.