AI, which isn't always 100% accurate, offers this...
"There is currently no built-in way in NCH PhotoPad to add the Clone/Stamp tool directly to the main page toolbar for one-click access. The tool is typically accessed by navigating to the "Tools" or "Retouch" tab, where you may need to scroll to find it.
If you use the Clone/Stamp tool often, consider keeping the "Tools" or "Retouch" tab open during your editing session to reduce extra clicks."
File a suggestion.