In the Safari sidebar select a folder then right click or Control+Click and a menu will appear. At the bottom of the menu is the option to sort by name or address. That sorts the contents of that folder only and does not sort the contents of any sub-folders. If you have sub-folders you will have to sort their contents folder by folder. (At least it works that way in Safari Technology Preview)

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein