how to navigate system dialogue boxes never touching the mouse?
If you've got one of the standard macOS file save sheets, such as:


  Do you want to save the changes you made in the document ‘untitled’?
  Don't Save | Cancel | Save



↩︎ enter will save.
⎋ esc will cancel.
⌘⌫ command-backspace will not save (usual Finder delete shortcut).


If the sheet is a slightly different macOS file save sheets, where the document has not been saved previously, then ⌘⌫ will select the Delete button from the options


  Delete | Cancel | Save


For macOS file save sheets which prompt for a destination to save the file, you can quickly jump to a standard folder using the following shortcuts:


⇧⌘O for ~/Documents
⌘D or ⇧⌘D for ~/Desktop
⇧⌘H for ~ (your home folder)
⌥⌘L for ~/Downloads
⇧⌘I for iCloud Drive
⇧⌘G or / or ~ to enter a path name by typing the path


Some of these shortcuts are described in the Apple KB article Mac keyboard shortcuts

The ‘don't save’ shortcut used to be ⌘D, however many save sheets have an option to specify the location for the document, in cases where the location is undefined. ⌘D chooses the Desktop for the destination. To revert macOS back to ⌘D for ‘don't save’, set the following key:

defaults write -g NSSavePanelStandardDesktopShortcutOnly -bool true